Diff: rfc8794xml2.original.xml

	rfc8794xml2.original.xml	rfc8794.xml

		<?xml version="1.0" encoding="UTF-8"?>
		<!DOCTYPE rfc SYSTEM "rfc2629-xhtml.ent">

		<rfc version="3" ipr="trust200902" docName="draft-ietf-cellar-ebml-20" sortRefs=
		"true" submissionType="IETF" category="std" xml:lang="en" xmlns:xi="http://www.w
		3.org/2001/XInclude" tocInclude="true" symRefs="true" consensus="true" number="8
		794">

		<front>
		<title abbrev="EBML">Extensible Binary Meta Language</title><seriesInfo value="8
		794" status="standard" name="RFC"></seriesInfo>
		<author initials="S." surname="Lhomme" fullname="Steve Lhomme"><address><postal>
		</postal><email>slhomme@matroska.org</email>
		</address></author>
		<author initials="D." surname="Rice" fullname="Dave Rice"><address><postal>
		</postal><email>dave@dericed.com</email>
		</address></author>
		<author initials="M." surname="Bunkus" fullname="Moritz Bunkus"><address><postal
		>
		</postal><email>moritz@bunkus.org</email>
		</address></author>
		<date year="2020" month="July"></date>
		<area>art</area>
		<workgroup>cellar</workgroup>
		<keyword>binary</keyword>
		<keyword>storage</keyword>
		<keyword>xml</keyword>
		<keyword>matroska</keyword>
		<keyword>webm</keyword>

		<abstract>
		<t>This document defines the Extensible Binary Meta Language (EBML) format as a
		binary container format designed for audio/video storage. EBML is designed as a
		binary equivalent to XML and uses a storage-efficient approach to build nested E
		lements with identifiers, lengths, and values. Similar to how an XML Schema defi
		nes the structure and semantics of an XML Document, this document defines how EB
		ML Schemas are created to convey the semantics of an EBML Document.</t>
		</abstract>

		</front>

		<middle>

		<section anchor="introduction"><name>Introduction</name>
		<t>EBML, short for Extensible Binary Meta Language, specifies a binary format
		aligned with octets (bytes) and inspired by the principle of XML (a framework fo
		r
		structuring data).</t>
		<t>The goal of this document is to define a generic, binary, space-efficient
		format that can be used to define more complex formats using an EBML
		Schema. EBML is used by the multimedia container, Matroska
		<xref target="I-D.ietf-cellar-matroska"></xref>. The applicability of EBML for o
		ther
		use cases is beyond the scope of this document.</t>
		<t>The definition of the EBML format recognizes the idea behind HTML and XML
		as a good one: separate structure and semantics allowing the same structural
		layer to be used with multiple, possibly widely differing, semantic
		layers. Except for the EBML Header and a few Global Elements, this
		specification does not define particular EBML format semantics; however, this
		specification is intended to define how other EBML-based formats can be
		defined, such as the audio/video container formats Matroska and WebM <xref targe
		t="WebM"></xref>.</t>
		<t>EBML uses a simple approach of building Elements upon three pieces of data (t
		ag, length, and value), as this approach is well known, easy to parse, and allow
		s selective data parsing. The EBML structure additionally allows for hierarchica
		l arrangement to support complex structural formats in an efficient manner.</t>
		<t>A typical EBML file has the following structure:</t>

		<artwork>EBML Header (master)
		+ DocType (string)
		+ DocTypeVersion (unsigned integer)
		EBML Body Root (master)
		+ ElementA (utf-8)
		+ Parent (master)
		+ ElementB (integer)
		+ Parent (master)
		+ ElementB (integer)
		</artwork>
		</section>

		<section anchor="notation-and-conventions"><name>Notation and Conventions</name>
		<t>The key words "<bcp14>MUST</bcp14>", "<bcp14>MUST NOT</bcp14>&
		quot;,
		"<bcp14>REQUIRED</bcp14>", "<bcp14>SHALL</bcp14>", "<bc
		p14>SHALL NOT</bcp14>",
		"<bcp14>SHOULD</bcp14>", "<bcp14>SHOULD NOT</bcp14>",
		"<bcp14>RECOMMENDED</bcp14>", "<bcp14>NOT RECOMMENDED</bcp14>&quo
		t;,
		"<bcp14>MAY</bcp14>", and "<bcp14>OPTIONAL</bcp14>" in this
		document are to be interpreted as
		described in BCP 14 <xref target="RFC2119"></xref> <xref target="RFC8174"><
		/xref>
		when, and only when, they appear in all capitals, as shown here.</t>
		<t>This document defines specific terms in order to define the format and
		application of <tt>EBML</tt>. Specific terms are defined below:</t>

		<dl>
		<dt><tt>EBML</tt>:</dt>
		<dd>Extensible Binary Meta Language</dd>
		<dt><tt>EBML Document Type</tt>:</dt>
		<dd>A name provided by an <tt>EBML Schema</tt> to designate a particular
		implementation of <tt>EBML</tt> for a data format (e.g., Matroska and WebM).</dd
		>
		<dt><tt>EBML Schema</tt>:</dt>
		<dd>A standardized definition for the structure of an <tt>EBML Document Type</tt
		>.</dd>
		<dt><tt>EBML Document</tt>:</dt>
		<dd>A datastream comprised of only two components, an <tt>EBML Header</tt> and
		an <tt>EBML Body</tt>.</dd>
		<dt><tt>EBML Reader</tt>:</dt>
		<dd>A data parser that interprets the semantics of an <tt>EBML Document</tt>
		and creates a way for programs to use <tt>EBML</tt>.</dd>
		<dt><tt>EBML Stream</tt>:</dt>
		<dd>A file that consists of one or more <tt>EBML Documents</tt> that are
		concatenated together.</dd>
		<dt><tt>EBML Header</tt>:</dt>
		<dd>A declaration that provides processing instructions and identification of
		the <tt>EBML Body</tt>. The <tt>EBML Header</tt> is analogous to an XML Declarat
		ion
		<xref target="XML"></xref> (see Section 2.8 on "Prolog and Document Type De
		claration").</dd>
		<dt><tt>EBML Body</tt>:</dt>
		<dd>All data of an <tt>EBML Document</tt> following the <tt>EBML Header</tt>.</d
		d>
		<dt><tt>Variable-Size Integer</tt>:</dt>
		<dd>A compact variable-length binary value that defines its own length.</dd>
		<dt><tt>VINT</tt>:</dt>
		<dd>Also known as <tt>Variable-Size Integer</tt>.</dd>
		<dt><tt>EBML Element</tt>:</dt>
		<dd>A foundation block of data that contains three parts: an <tt>Element ID</tt>
		,
		an <tt>Element Data Size</tt>, and <tt>Element Data</tt>.</dd>
		<dt><tt>Element ID</tt>:</dt>
		<dd>A binary value, encoded as a <tt>Variable-Size Integer</tt>,
		used to uniquely identify a defined <tt>EBML Element</tt> within a specific
		<tt>EBML Schema</tt>.</dd>
		<dt><tt>Element Data Size</tt>:</dt>
		<dd>An expression, encoded as a <tt>Variable-Size Integer</tt>, of the length
		in octets of <tt>Element Data</tt>.</dd>
		<dt><tt>VINTMAX</tt>:</dt>
		<dd>The maximum possible value that can be stored as <tt>Element Data Size</tt>.
		</dd>
		<dt><tt>Unknown-Sized Element</tt>:</dt>
		<dd>An <tt>Element</tt> with an unknown <tt>Element Data Size</tt>.</dd>
		<dt><tt>Element Data</tt>:</dt>
		<dd>The value(s) of the <tt>EBML Element</tt>, which is identified by its
		<tt>Element ID</tt> and <tt>Element Data Size</tt>. The form of the <tt>Element
		Data</tt> is
		defined by this document and the corresponding <tt>EBML Schema</tt> of the
		Element's <tt>EBML Document Type</tt>.</dd>
		<dt><tt>Root Level</tt>:</dt>
		<dd>The starting level in the hierarchy of an <tt>EBML Document</tt>.</dd>
		<dt><tt>Root Element</tt>:</dt>
		<dd>A mandatory, nonrepeating <tt>EBML Element</tt> that occurs at the top
		level of the path hierarchy within an <tt>EBML Body</tt> and contains all other
		<tt>EBML Elements</tt> of the <tt>EBML Body</tt>, excepting optional <tt>Void El
		ements</tt>.</dd>
		<dt><tt>Top-Level Element</tt>:</dt>
		<dd>An <tt>EBML Element</tt> defined to only occur as a <tt>Child Element</tt>
		of the <tt>Root Element</tt>.</dd>
		<dt><tt>Master Element</tt>:</dt>
		<dd>The <tt>Master Element</tt> contains zero, one, or many other <tt>EBML Eleme
		nts</tt>.</dd>
		<dt><tt>Child Element</tt>:</dt>
		<dd>A <tt>Child Element</tt> is a relative term to describe the <tt>EBML Element
		s</tt>
		immediately contained within a <tt>Master Element</tt>.</dd>
		<dt><tt>Parent Element</tt>:</dt>
		<dd>A relative term to describe the <tt>Master Element</tt> that contains a
		specified element. For any specified <tt>EBML Element</tt> that is not at
		<tt>Root Level</tt>, the <tt>Parent Element</tt> refers to the <tt>Master Elemen
		t</tt>
		in which that <tt>EBML Element</tt> is directly contained.</dd>
		<dt><tt>Descendant Element</tt>:</dt>
		<dd>A relative term to describe any <tt>EBML Elements</tt> contained within a
		<tt>Master Element</tt>, including any of the <tt>Child Elements</tt> of its
		<tt>Child Elements</tt>, and so on.</dd>
		<dt><tt>Void Element</tt>:</dt>
		<dd>An <tt>Element</tt> used to overwrite data or
		reserve space within a <tt>Master Element</tt> for later use.</dd>
		<dt><tt>Element Name</tt>:</dt>
		<dd>The human-readable name of the <tt>EBML Element</tt>.</dd>
		<dt><tt>Element Path</tt>:</dt>
		<dd>The hierarchy of <tt>Parent Element</tt> where the <tt>EBML Element</tt>
		is expected to be found in the <tt>EBML Body</tt>.</dd>
		<dt><tt>Empty Element</tt>:</dt>
		<dd>An <tt>EBML Element</tt> that has an <tt>Element Data Size</tt> with all
		<tt>VINT_DATA</tt> bits set to zero, which indicates
		that the <tt>Element Data</tt> of the <tt>Element</tt> is zero octets in
		length.</dd>
		</dl>
		</section>

		<section anchor="structure"><name>Structure</name>
		<t>EBML uses a system of Elements to compose an EBML Document. EBML Elements inc
		orporate three parts: an Element ID, an Element Data Size, and Element Data. The
		Element Data, which is described by the Element ID, includes either binary data
		, one or more other EBML Elements, or both.</t>
		</section>

		<section anchor="variable-size-integer"><name>Variable-Size Integer</name>
		<t>The Element ID and Element Data Size are both encoded as a Variable-Size
		Integer. The Variable-Size Integer is composed of a VINT_WIDTH, VINT_MARKER,
		and VINT_DATA, in that order. Variable-Size Integers <bcp14>MUST</bcp14>
		left-pad the VINT_DATA value with zero bits so that the whole Variable-Size
		Integer is octet aligned. The Variable-Size Integer will be referred to as
		VINT for shorthand.</t>

		<section anchor="vint-width"><name>VINT_WIDTH</name>
		<t>Each Variable-Size Integer starts with a VINT_WIDTH followed by a
		VINT_MARKER. VINT_WIDTH is a sequence of zero or more bits of value <tt>0</tt>
		and is terminated by the VINT_MARKER, which is a single bit of value
		<tt>1</tt>. The total length in bits of both VINT_WIDTH and VINT_MARKER is the
		total length in octets in of the Variable-Size Integer.</t>
		<t>The single bit <tt>1</tt> starts a Variable-Size Integer with a length of
		one octet. The sequence of bits <tt>01</tt> starts a Variable-Size Integer
		with a length of two octets. <tt>001</tt> starts a Variable-Size Integer with
		a length of three octets, and so on, with each additional <tt>0</tt> bit adding
		one
		octet to the length of the Variable-Size Integer.</t>
		</section>

		<section anchor="vint-marker"><name>VINT_MARKER</name>
		<t>The VINT_MARKER serves as a separator between the VINT_WIDTH and VINT_DATA. E
		ach Variable-Size Integer <bcp14>MUST</bcp14> contain exactly one VINT_MARKER. T
		he VINT_MARKER is one bit in length and contain a bit with a value of one. The f
		irst bit with a value of one within the Variable-Size Integer is the VINT_MARKER
		.</t>
		</section>

		<section anchor="vint-data"><name>VINT_DATA</name>
		<t>The VINT_DATA portion of the Variable-Size Integer includes all data followin
		g
		(but not including) the VINT_MARKER until end of the Variable-Size
		Integer whose length is derived from the VINT_WIDTH. The bits required for the
		VINT_WIDTH and the VINT_MARKER use one out of every eight bits of the total
		length of the Variable-Size Integer. Thus, a Variable-Size Integer of 1-octet
		length supplies 7 bits for VINT_DATA, a 2-octet length supplies 14 bits for
		VINT_DATA, and a 3-octet length supplies 21 bits for VINT_DATA. If the number
		of bits required for VINT_DATA is less than the bit size of VINT_DATA, then
		VINT_DATA <bcp14>MUST</bcp14> be zero-padded to the left to a size that
		fits. The VINT_DATA value <bcp14>MUST</bcp14> be expressed as a big-endian
		unsigned integer.</t>
		</section>

		<section anchor="vint-examples"><name>VINT Examples</name>
		<t><xref target="tableUsableBits"></xref> shows examples of Variable-Size
		Integers with lengths from 1 to 5 octets. The "Usable Bits" column ref
		ers to the
		number of bits that can be used in the VINT_DATA. The "Representation"
		column
		depicts a binary expression of Variable-Size Integers where VINT_WIDTH is
		depicted by <tt>0</tt>, the VINT_MARKER as <tt>1</tt>, and the VINT_DATA as
		<tt>x</tt>.</t>
		<table anchor="tableUsableBits"><name>VINT examples depicting usable bits</name>
		<thead>
		<tr>
		<th>Octet Length</th>
		<th>Usable Bits</th>
		<th align="left">Representation</th>
		</tr>
		</thead>

		<tbody>
		<tr>
		<td>1</td>
		<td>7</td>
		<td align="left">1xxx xxxx</td>
		</tr>

		<tr>
		<td>2</td>
		<td>14</td>
		<td align="left">01xx xxxx xxxx xxxx</td>
		</tr>

		<tr>
		<td>3</td>
		<td>21</td>
		<td align="left">001x xxxx xxxx xxxx xxxx xxxx</td>
		</tr>

		<tr>
		<td>4</td>
		<td>28</td>
		<td align="left">0001 xxxx xxxx xxxx xxxx xxxx xxxx xxxx</td>
		</tr>

		<tr>
		<td>5</td>
		<td>35</td>
		<td align="left">0000 1xxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx</td>
		</tr>
		</tbody>
		</table><t>A Variable-Size Integer may be rendered at octet lengths larger
		than needed to store the data in order to facilitate overwriting it at a later
		date -- e.g., when its final size isn't known in advance. In
		<xref target="tableVariousSizes"></xref>, an integer <tt>2</tt> (with a
		corresponding binary value of 0b10) is shown encoded as different Variable-Size
		Integers with lengths from one octet to four octets. All four encoded
		examples have identical semantic meaning, though the VINT_WIDTH and the padding
		of the VINT_DATA vary.</t>
		<table anchor="tableVariousSizes"><name>VINT examples depicting the same
		integer value rendered at different VINT lengths</name>
		<thead>
		<tr>
		<th>Integer</th>
		<th>Octet Length</th>
		<th align="right">As Represented in VINT (binary)</th>
		<th align="right">As Represented in VINT (hexadecimal)</th>
		</tr>
		</thead>

		<tbody>
		<tr>
		<td>2</td>
		<td>1</td>
		<td align="right">1000 0010</td>
		<td align="right">0x82</td>
		</tr>

		<tr>
		<td>2</td>
		<td>2</td>
		<td align="right">0100 0000 0000 0010</td>
		<td align="right">0x4002</td>
		</tr>

		<tr>
		<td>2</td>
		<td>3</td>
		<td align="right">0010 0000 0000 0000 0000 0010</td>
		<td align="right">0x200002</td>
		</tr>

		<tr>
		<td>2</td>
		<td>4</td>
		<td align="right">0001 0000 0000 0000 0000 0000 0000 0010</td>
		<td align="right">0x10000002</td>
		</tr>
		</tbody>
		</table></section>
		</section>

		<section anchor="element-id"><name>Element ID</name>
		<t>An Element ID is a Variable-Size Integer. By default, Element IDs are from
		one octet to four octets in length, although Element IDs of greater lengths
		<bcp14>MAY</bcp14> be used if the EBMLMaxIDLength Element of the EBML Header
		is set to a value greater than four (see
		<xref target="ebmlmaxidlength-element"></xref>). The bits of the VINT_DATA compo
		nent
		of the Element ID <bcp14>MUST NOT</bcp14> be all <tt>0</tt> values or all
		<tt>1</tt> values. The VINT_DATA component of the Element ID
		<bcp14>MUST</bcp14> be encoded at the shortest valid length. For example, an
		Element ID with binary encoding of <tt>1011 1111</tt> is valid, whereas an
		Element ID with binary encoding of <tt>0100 0000 0011 1111</tt> stores a
		semantically equal VINT_DATA but is invalid, because a shorter VINT encoding is
		possible. Additionally, an Element ID with binary encoding of <tt>1111 1111</tt>
		is invalid, since the VINT_DATA section is set to all one values,
		whereas an Element ID with binary encoding of <tt>0100 0000 0111 1111</tt>
		stores a semantically equal VINT_DATA and is the shortest-possible VINT
		encoding.</t>
		<t><xref target="tableElementIDValidity"></xref> details these specific examples
		further:</t>
		<table anchor="tableElementIDValidity"><name>Examples of valid and invalid Eleme
		nt IDs</name>
		<thead>
		<tr>
		<th align="right">VINT_WIDTH</th>
		<th align="right">VINT_MARKER</th>
		<th align="right">VINT_DATA</th>
		<th align="left">Element ID Status</th>
		</tr>
		</thead>

		<tbody>
		<tr>
		<td align="right"></td>
		<td align="right">1</td>
		<td align="right">0000000</td>
		<td align="left">Invalid: VINT_DATA <bcp14>MUST NOT</bcp14> be set to all 0</td>
		</tr>

		<tr>
		<td align="right">0</td>
		<td align="right">1</td>
		<td align="right">00000000000000</td>
		<td align="left">Invalid: VINT_DATA <bcp14>MUST NOT</bcp14> be set to all 0</td>
		</tr>

		<tr>
		<td align="right"></td>
		<td align="right">1</td>
		<td align="right">0000001</td>
		<td align="left">Valid</td>
		</tr>

		<tr>
		<td align="right">0</td>
		<td align="right">1</td>
		<td align="right">00000000000001</td>
		<td align="left">Invalid: A shorter VINT_DATA encoding is available.</td>
		</tr>

		<tr>
		<td align="right"></td>
		<td align="right">1</td>
		<td align="right">0111111</td>
		<td align="left">Valid</td>
		</tr>

		<tr>
		<td align="right">0</td>
		<td align="right">1</td>
		<td align="right">00000000111111</td>
		<td align="left">Invalid: A shorter VINT_DATA encoding is available.</td>
		</tr>

		<tr>
		<td align="right"></td>
		<td align="right">1</td>
		<td align="right">1111111</td>
		<td align="left">Invalid: VINT_DATA <bcp14>MUST NOT</bcp14> be set to all 1</td>
		</tr>

		<tr>
		<td align="right">0</td>
		<td align="right">1</td>
		<td align="right">00000001111111</td>
		<td align="left">Valid</td>
		</tr>
		</tbody>
		</table><t>The range and count of possible Element IDs are determined by their
		octet length. Examples of this are provided in
		<xref target="tableElementIDRanges"></xref>.</t>
		<table anchor="tableElementIDRanges"><name>Examples of count and range for
		Element IDs at various octet lengths</name>
		<thead>
		<tr>
		<th align="center">Element ID Octet Length</th>
		<th align="center">Range of Valid Element IDs</th>
		<th align="right">Number of Valid Element IDs</th>
		</tr>
		</thead>

		<tbody>
		<tr>
		<td align="center">1</td>
		<td align="center">0x81 - 0xFE</td>
		<td align="right">126</td>
		</tr>

		<tr>
		<td align="center">2</td>
		<td align="center">0x407F - 0x7FFE</td>
		<td align="right">16,256</td>
		</tr>

		<tr>
		<td align="center">3</td>
		<td align="center">0x203FFF - 0x3FFFFE</td>
		<td align="right">2,080,768</td>
		</tr>

		<tr>
		<td align="center">4</td>
		<td align="center">0x101FFFFF - 0x1FFFFFFE</td>
		<td align="right">268,338,304</td>
		</tr>
		</tbody>
		</table></section>

		<section anchor="element-data-size"><name>Element Data Size</name>

		<section anchor="data-size-format"><name>Data Size Format</name>
		<t>The Element Data Size expresses the length in octets of Element Data. The
		Element Data Size itself is encoded as a Variable-Size Integer. By default,
		Element Data Sizes can be encoded in lengths from one octet to eight octets,
		although Element Data Sizes of greater lengths <bcp14>MAY</bcp14> be used if
		the octet length of the longest Element Data Size of the EBML Document is
		declared in the EBMLMaxSizeLength Element of the EBML Header (see
		<xref target="ebmlmaxsizelength-element"></xref>). Unlike the VINT_DATA of the
		Element ID, the VINT_DATA component of the Element Data Size is not mandated
		to be encoded at the shortest valid length. For example, an Element Data Size
		with binary encoding of 1011 1111 or a binary encoding of 0100 0000 0011 1111
		are both valid Element Data Sizes and both store a semantically equal value
		(both 0b00000000111111 and 0b0111111, the VINT_DATA sections of the examples,
		represent the integer 63).</t>
		<t>Although an Element ID with all VINT_DATA bits set to zero is invalid, an
		Element Data Size with all VINT_DATA bits set to zero is allowed for EBML
		Element Types that do not mandate a nonzero length (see
		<xref target="ebml-element-types"></xref>). An Element Data Size with all VINT_D
		ATA
		bits set to zero indicates that the Element Data is zero octets in
		length. Such an EBML Element is referred to as an Empty Element. If an Empty
		Element has a default value declared, then the EBML Reader <bcp14>MUST</bcp14>
		interpret the value of the Empty Element as the default value. If an Empty
		Element has no default value declared, then the EBML Reader <bcp14>MUST</bcp14>
		use the value of the Empty Element for the corresponding EBML Element Type of
		the Element ID, 0 for numbers and an empty string for strings.</t>
		</section>

		<section anchor="unknown-data-size"><name>Unknown Data Size</name>
		<t>An Element Data Size with all VINT_DATA bits set to one is reserved as an
		indicator that the size of the EBML Element is unknown. The only reserved
		value for the VINT_DATA of Element Data Size is all bits set to one. An EBML
		Element with an unknown Element Data Size is referred to as an Unknown-Sized
		Element. Only a Master Element is allowed to be of unknown size, and it can
		only be so if the <tt>unknownsizeallowed</tt> attribute of its EBML Schema is
		set to true (see <xref target="unknownsizeallowed"></xref>).</t>
		<t>The use of Unknown-Sized Elements allows an EBML Element to be written and re
		ad before the size of the EBML Element is known. Unknown-Sized Elements <bcp14>M
		UST</bcp14> only be used if the Element Data Size is not known before the Elemen
		t Data is written, such as in some cases of datastreaming. The end of an Unknown
		-Sized Element is determined by whichever comes first:</t>

		<ul>
		<li><t>Any EBML Element that is a valid Parent Element of the Unknown-Sized Elem
		ent according to the EBML Schema, Global Elements excluded.</t>
		</li>
		<li><t>Any valid EBML Element according to the EBML Schema, Global Elements
		excluded, that is not a Descendant Element of the Unknown-Sized Element but
		shares a common direct parent, such as a Top-Level Element.</t>
		</li>
		<li><t>Any EBML Element that is a valid Root Element according to the EBML Schem
		a, Global Elements excluded.</t>
		</li>
		<li><t>The end of the Parent Element with a known size has been reached.</t>
		</li>
		<li><t>The end of the EBML Document, either when reaching the end of the file or
		because a new EBML Header started.</t>
		</li>
		</ul>
		<t>Consider an Unknown-Sized Element whose EBML path is
		<tt>\root\level1\level2\elt</tt>. When reading a new Element ID, assuming the
		EBML Path of that new Element is valid, here are some possible and impossible
		ways that this new Element is ending <tt>elt</tt>:</t>
		<table><name>Examples of determining the end of an Unknown-Sized Element
		</name>
		<thead>
		<tr>
		<th align="left">EBML Path of new element</th>
		<th align="left">Status</th>
		</tr>
		</thead>

		<tbody>
		<tr>
		<td align="left"><tt>\root\level1\level2</tt></td>
		<td align="left">Ends the Unknown-Sized Element, as it is a new Parent Element</
		td>
		</tr>

		<tr>
		<td align="left"><tt>\root\level1</tt></td>
		<td align="left">Ends the Unknown-Sized Element, as it is a new Parent Element</
		td>
		</tr>

		<tr>
		<td align="left"><tt>\root</tt></td>
		<td align="left">Ends the Unknown-Sized Element, as it is a new Root Element</td
		>
		</tr>

		<tr>
		<td align="left"><tt>\root2</tt></td>
		<td align="left">Ends the Unknown-Sized Element, as it is a new Root Element</td
		>
		</tr>

		<tr>
		<td align="left"><tt>\root\level1\level2\other</tt></td>
		<td align="left">Ends the Unknown-Sized Element, as they share the same parent</
		td>
		</tr>

		<tr>
		<td align="left"><tt>\root\level1\level2\elt</tt></td>
		<td align="left">Ends the Unknown-Sized Element, as they share the same parent</
		td>
		</tr>

		<tr>
		<td align="left"><tt>\root\level1\level2\elt\inside</tt></td>
		<td align="left">Doesn't end the Unknown-Sized Element; it's a child of <tt>elt<
		/tt></td>
		</tr>

		<tr>
		<td align="left"><tt>\root\level1\level2\elt\<global></tt></td>
		<td align="left">Global Element is valid; it's a child of <tt>elt</tt></td>
		</tr>

		<tr>
		<td align="left"><tt>\root\level1\level2\<global></tt></td>
		<td align="left">Global Element cannot be interpreted with this path; while pars
		ing <tt>elt</tt>, a Global Element can only be a child of <tt>elt</tt></td>
		</tr>
		</tbody>
		</table></section>

		<section anchor="data-size-values"><name>Data Size Values</name>
		<t>For Element Data Sizes encoded at octet lengths from one to eight,
		<xref target="tableVintRangePerLength"></xref> depicts the range of possible val
		ues
		that can be encoded as an Element Data Size. An Element Data Size with an
		octet length of 8 is able to express a size of 2<sup>56</sup>-2 or
		72,057,594,037,927,934 octets (or about 72 petabytes). The maximum possible
		value that can be stored as Element Data Size is referred to as VINTMAX.</t>
		<table anchor="tableVintRangePerLength"><name>Possible range of values that
		can be stored in VINTs, by octet length</name>
		<thead>
		<tr>
		<th>Octet Length</th>
		<th>Possible Value Range</th>
		</tr>
		</thead>

		<tbody>
		<tr>
		<td>1</td>
		<td>0 to 2<sup>7</sup> - 2</td>
		</tr>

		<tr>
		<td>2</td>
		<td>0 to 2<sup>14</sup> - 2</td>
		</tr>

		<tr>
		<td>3</td>
		<td>0 to 2<sup>21</sup> - 2</td>
		</tr>

		<tr>
		<td>4</td>
		<td>0 to 2<sup>28</sup> - 2</td>
		</tr>

		<tr>
		<td>5</td>
		<td>0 to 2<sup>35</sup> - 2</td>
		</tr>

		<tr>
		<td>6</td>
		<td>0 to 2<sup>42</sup> - 2</td>
		</tr>

		<tr>
		<td>7</td>
		<td>0 to 2<sup>49</sup> - 2</td>
		</tr>

		<tr>
		<td>8</td>
		<td>0 to 2<sup>56</sup> - 2</td>
		</tr>
		</tbody>
		</table><t>If the length of Element Data equals 2<sup>n*7</sup>-1, then the octe
		t
		length of the Element Data Size <bcp14>MUST</bcp14> be at least n+1. This rule
		prevents an Element Data Size from being expressed as the unknown-size
		value. <xref target="tableVintReservation"></xref> clarifies this rule by
		showing a valid and invalid expression of an Element Data Size with a
		VINT_DATA of 127 (which is equal to 2<sup>1*7</sup>-1) and 16,383 (which is equa
		l to
		2<sup>2*7</sup>-1).</t>
		<table anchor="tableVintReservation"><name>Demonstration of VINT_DATA
		reservation for VINTs of unknown size</name>
		<thead>
		<tr>
		<th align="right">VINT_WIDTH</th>
		<th align="right">VINT_MARKER</th>
		<th align="right">VINT_DATA</th>
		<th>Element Data Size Status</th>
		</tr>
		</thead>

		<tbody>
		<tr>
		<td align="right"></td>
		<td align="right">1</td>
		<td align="right">1111111</td>
		<td>Reserved (meaning Unknown)</td>
		</tr>

		<tr>
		<td align="right">0</td>
		<td align="right">1</td>
		<td align="right">00000001111111</td>
		<td>Valid (meaning 127 octets)</td>
		</tr>

		<tr>
		<td align="right">00</td>
		<td align="right">1</td>
		<td align="right">000000000000001111111</td>
		<td>Valid (meaning 127 octets)</td>
		</tr>

		<tr>
		<td align="right">0</td>
		<td align="right">1</td>
		<td align="right">11111111111111</td>
		<td>Reserved (meaning Unknown)</td>
		</tr>

		<tr>
		<td align="right">00</td>
		<td align="right">1</td>
		<td align="right">000000011111111111111</td>
		<td>Valid (16,383 octets)</td>
		</tr>
		</tbody>
		</table></section>
		</section>

		<section anchor="ebml-element-types"><name>EBML Element Types</name>
		<t>EBML Elements are defined by an EBML Schema (see
		<xref target="ebml-schema"></xref>), which <bcp14>MUST</bcp14> declare one of th
		e
		following EBML Element Types for each EBML Element. An EBML Element Type
		defines a concept of storing data within an EBML Element that describes such
		characteristics as length, endianness, and definition.</t>
		<t>EBML Elements that are defined as a Signed Integer Element, Unsigned
		Integer Element, Float Element, or Date Element use big-endian storage.</t>

		<section anchor="signed-integer-element"><name>Signed Integer Element</name>
		<t>A Signed Integer Element <bcp14>MUST</bcp14> declare a length from zero to ei
		ght octets. If the EBML Element is not defined to have a default value, then a S
		igned Integer Element with a zero-octet length represents an integer value of ze
		ro.</t>
		<t>A Signed Integer Element stores an integer (meaning that it can be written
		without a fractional component) that could be negative, positive, or
		zero. Signed Integers are stored with two's complement notation with the
		leftmost bit being the sign bit. Because EBML limits Signed Integers to 8
		octets in length, a Signed Integer Element stores a number from
		-9,223,372,036,854,775,808 to +9,223,372,036,854,775,807.</t>
		</section>

		<section anchor="unsigned-integer-element"><name>Unsigned Integer Element</name>
		<t>An Unsigned Integer Element <bcp14>MUST</bcp14> declare a length from zero to
		eight octets. If the EBML Element is not defined to have a default value, then
		an Unsigned Integer Element with a zero-octet length represents an integer value
		of zero.</t>
		<t>An Unsigned Integer Element stores an integer (meaning that it can be
		written without a fractional component) that could be positive or
		zero. Because EBML limits Unsigned Integers to 8 octets in length, an Unsigned
		Integer Element stores a number from 0 to 18,446,744,073,709,551,615.</t>
		</section>

		<section anchor="float-element"><name>Float Element</name>
		<t>A Float Element <bcp14>MUST</bcp14> declare a length of either zero octets
		(0 bit), four octets (32 bit), or eight octets (64 bit). If the EBML Element
		is not defined to have a default value, then a Float Element with a zero-octet
		length represents a numerical value of zero.</t>
		<t>A Float Element stores a floating-point number in the 32-bit and 64-bit
		binary interchange format, as defined in <xref target="IEEE.754"></xref>.</t>
		</section>

		<section anchor="string-element"><name>String Element</name>
		<t>A String Element <bcp14>MUST</bcp14> declare a length in octets from zero to
		VINTMAX. If the EBML Element is not defined to have a default value, then a Stri
		ng Element with a zero-octet length represents an empty string.</t>
		<t>A String Element <bcp14>MUST</bcp14> either be empty (zero-length) or contain
		printable ASCII characters <xref target="RFC0020"></xref> in the range of 0x20
		to 0x7E, with an exception made for termination (see <xref target="terminating-e
		lements"></xref>).</t>
		</section>

		<section anchor="utf-8-element"><name>UTF-8 Element</name>
		<t>A UTF-8 Element <bcp14>MUST</bcp14> declare a length in octets from zero to V
		INTMAX. If the EBML Element is not defined to have a default value, then a UTF-8
		Element with a zero-octet length represents an empty string.</t>
		<t>A UTF-8 Element contains only a valid Unicode string as defined in <xref targ
		et="RFC3629"></xref>, with an exception made for termination (see <xref target="
		terminating-elements"></xref>).</t>
		</section>

		<section anchor="date-element"><name>Date Element</name>
		<t>A Date Element <bcp14>MUST</bcp14> declare a length of either zero octets or
		eight octets. If the EBML Element is not defined to have a default value, then a
		Date Element with a zero-octet length represents a timestamp of 2001-01-01T00:0
		0:00.000000000 UTC <xref target="RFC3339"></xref>.</t>
		<t>The Date Element stores an integer in the same format as the Signed Integer E
		lement that expresses a point in time referenced in nanoseconds from the precise
		beginning of the third millennium of the Gregorian Calendar in Coordinated Univ
		ersal Time (also known as 2001-01-01T00:00:00.000000000 UTC). This provides a po
		ssible expression of time from 1708-09-11T00:12:44.854775808 UTC to 2293-04-11T1
		1:47:16.854775807 UTC.</t>
		</section>

		<section anchor="master-element"><name>Master Element</name>
		<t>A Master Element <bcp14>MUST</bcp14> declare a length in octets from zero to
		VINTMAX or be of unknown length. See <xref target="element-data-size"></xref> fo
		r rules that apply to elements of unknown length.</t>
		<t>The Master Element contains zero or more other elements. EBML Elements contai
		ned within a Master Element <bcp14>MUST</bcp14> have the EBMLParentPath of their
		Element Path equal to the EBMLFullPath of the Master Element Element Path (see
		<xref target="path"></xref>). Element Data stored within Master Elements <bcp14>
		SHOULD</bcp14> only consist of EBML Elements and <bcp14>SHOULD NOT</bcp14> conta
		in any data that is not part of an EBML Element. The EBML Schema identifies what
		Element IDs are valid within the Master Elements for that version of the EBML D
		ocument Type. Any data contained within a Master Element that is not part of a C
		hild Element <bcp14>MUST</bcp14> be ignored.</t>
		</section>

		<section anchor="binary-element"><name>Binary Element</name>
		<t>A Binary Element <bcp14>MUST</bcp14> declare a length in octets from zero to
		VINTMAX.</t>
		<t>The contents of a Binary Element should not be interpreted by the EBML Reader
		.</t>
		</section>
		</section>

		<section anchor="ebml-document"><name>EBML Document</name>
		<t>An EBML Document is composed of only two components, an EBML Header and an EB
		ML Body. An EBML Document <bcp14>MUST</bcp14> start with an EBML Header that dec
		lares significant characteristics of the entire EBML Body. An EBML Document cons
		ists of EBML Elements and <bcp14>MUST NOT</bcp14> contain any data that is not p
		art of an EBML Element.</t>

		<section anchor="ebml-header"><name>EBML Header</name>
		<t>The EBML Header is a declaration that provides processing instructions and id
		entification of the EBML Body. The EBML Header of an EBML Document is analogous
		to the XML Declaration of an XML Document.</t>
		<t>The EBML Header documents the EBML Schema (also known as the EBML DocType)
		that is used to semantically interpret the structure and meaning of the EBML
		Document. Additionally, the EBML Header documents the versions of both EBML
		and the EBML Schema that were used to write the EBML Document and the versions
		required to read the EBML Document.</t>
		<t>The EBML Header <bcp14>MUST</bcp14> contain a single Master Element with an
		Element Name of <tt>EBML</tt> and Element ID of <tt>0x1A45DFA3</tt> (see
		<xref target="ebml-element"></xref>); the Master Element may have any number of
		additional EBML Elements within it. The EBML Header of an EBML Document that
		uses an EBMLVersion of 1 <bcp14>MUST</bcp14> only contain EBML Elements that
		are defined as part of this document.</t>
		<t>Elements within an EBML Header can be at most 4 octets long, except for the
		EBML Element with Element Name <tt>EBML</tt> and Element ID
		<tt>0x1A45DFA3</tt> (see <xref target="ebml-element"></xref>); this Element can
		be up
		to 8 octets long.</t>
		</section>

		<section anchor="ebml-body"><name>EBML Body</name>
		<t>All data of an EBML Document following the EBML Header is the EBML Body. The
		end of the EBML Body, as well as the end of the EBML Document that contains the
		EBML Body, is reached at whichever comes first: the beginning of a new EBML Head
		er at the Root Level or the end of the file. This document defines precisely whi
		ch EBML Elements are to be used within the EBML Header but does not name or defi
		ne which EBML Elements are to be used within the EBML Body. The definition of wh
		ich EBML Elements are to be used within the EBML Body is defined by an EBML Sche
		ma.</t>
		<t>Within the EBML Body, the maximum octet length allowed for any Element ID
		is set by the EBMLMaxIDLength Element of the EBML Header, and the maximum octet
		length allowed for any Element Data Size is set by the EBMLMaxSizeLength
		Element of the EBML Header.</t>
		</section>
		</section>

		<section anchor="ebml-stream"><name>EBML Stream</name>
		<t>An EBML Stream is a file that consists of one or more EBML Documents that are
		concatenated together. An occurrence of an EBML Header at the Root Level marks
		the beginning of an EBML Document.</t>
		</section>

		<section anchor="ebml-versioning"><name>EBML Versioning</name>
		<t>An EBML Document handles 2 different versions: the version of the EBML Header
		and the version of the EBML Body. Both versions are meant to be backward compat
		ible.</t>

		<section anchor="ebml-header-version"><name>EBML Header Version</name>
		<t>The version of the EBML Header is found in EBMLVersion. An EBML parser can re
		ad an EBML Header if it can read either the EBMLVersion version or a version equ
		al or higher than the one found in EBMLReadVersion.</t>
		</section>

		<section anchor="ebml-document-version"><name>EBML Document Version</name>
		<t>The version of the EBML Body is found in EBMLDocTypeVersion. A parser for the
		particular DocType format can read the EBML Document if it can read either the
		EBMLDocTypeVersion version of that format or a version equal or higher than the
		one found in EBMLDocTypeReadVersion.</t>
		</section>
		</section>

		<section anchor="elements-semantics"><name>Elements semantics</name>

		<section anchor="ebml-schema"><name>EBML Schema</name>
		<t>An EBML Schema is a well-formed XML Document
		<xref target="XML"></xref> that defines the properties,
		arrangement, and usage of EBML Elements that compose a specific EBML Document
		Type. The relationship of an EBML Schema to an EBML Document is analogous to
		the relationship of an XML Schema <xref target="XML-SCHEMA"></xref> to an XML
		Document <xref target="XML"></xref>. An EBML Schema
		<bcp14>MUST</bcp14> be clearly associated with one or more EBML Document
		Types. An EBML Document Type is identified by a string stored within the EBML
		Header in the DocType Element -- for example, Matroska or WebM (see
		<xref target="doctype-element"></xref>). The DocType value for an EBML Document
		Type
		<bcp14>MUST</bcp14> be unique, persistent, and described in the IANA registry
		(see <xref target="ebml-doctypes-registry"></xref>).</t>
		<t>An EBML Schema <bcp14>MUST</bcp14> declare exactly one EBML Element at Root L
		evel (referred to as the Root Element) that occurs exactly once within an EBML D
		ocument. The Void Element <bcp14>MAY</bcp14> also occur at Root Level but is not
		a Root Element (see <xref target="void-element"></xref>).</t>
		<t>The EBML Schema <bcp14>MUST</bcp14> document all Elements of the EBML
		Body. The EBML Schema does not document Global Elements that are defined by
		this document (namely, the Void Element and the CRC-32 Element).</t>
		<t>The EBML Schema <bcp14>MUST NOT</bcp14> use the Element ID
		<tt>0x1A45DFA3</tt>, which is reserved for the EBML Header for the purpose of
		resynchronization.</t>
		<t>An EBML Schema <bcp14>MAY</bcp14> constrain the use of EBML Header Elements
		(see <xref target="ebml-header-elements"></xref>) by adding or constraining
		that Element's <tt>range</tt> attribute. For example, an EBML Schema
		<bcp14>MAY</bcp14> constrain the EBMLMaxSizeLength to a maximum value of
		<tt>8</tt> or <bcp14>MAY</bcp14> constrain the EBMLVersion to only support a
		value of <tt>1</tt>. If an EBML Schema adopts the EBML Header Element as is,
		then it is not required to document that Element within the EBML Schema. If an
		EBML Schema constrains the range of an EBML Header Element, then that Element
		<bcp14>MUST</bcp14> be documented within an <tt><element></tt> node of
		the EBML Schema. This document provides an example of an EBML Schema; see
		<xref target="ebml-schema-example"></xref>.</t>

		<section anchor="ebml-schema-example"><name>EBML Schema Example</name>

		<sourcecode type="xml"><?xml version="1.0" encoding="utf-8&quo
		t;?>
		<EBMLSchema xmlns="urn:ietf:rfc:8794"
		docType="files-in-ebml-demo" version="1">
		<!-- constraints to the range of two EBML Header Elements -->
		<element name="EBMLReadVersion" path="\EBML\EBMLReadVersion&q
		uot;
		id="0x42F7" minOccurs="1" maxOccurs="1" range=&
		quot;1" default="1"
		type="uinteger"/>
		<element name="EBMLMaxSizeLength"
		path="\EBML\EBMLMaxSizeLength" id="0x42F3" minOccurs=&quo
		t;1"
		maxOccurs="1" range="8" default="8" type="
		uinteger"/>
		<!-- Root Element-->
		<element name="Files" path="\Files" id="0x1946696C&
		quot;
		type="master">
		<documentation lang="en"
		purpose="definition">Container of data and
		attributes representing one or many files.</documentation>
		</element>
		<element name="File" path="\Files\File" id="0x6146&
		quot;
		type="master" minOccurs="1">
		<documentation lang="en" purpose="definition">
		An attached file.
		</documentation>
		</element>
		<element name="FileName" path="\Files\File\FileName"
		id="0x614E" type="utf-8"
		minOccurs="1">
		<documentation lang="en" purpose="definition">
		Filename of the attached file.
		</documentation>
		</element>
		<element name="MimeType" path="\Files\File\MimeType"
		id="0x464D" type="string"
		minOccurs="1">
		<documentation lang="en" purpose="definition">
		MIME type of the file.
		</documentation>
		</element>
		<element name="ModificationTimestamp"
		path="\Files\File\ModificationTimestamp" id="0x4654"
		type="date" minOccurs="1">
		<documentation lang="en" purpose="definition">
		Modification timestamp of the file.
		</documentation>
		</element>
		<element name="Data" path="\Files\File\Data" id="0x
		4664"
		type="binary" minOccurs="1">
		<documentation lang="en" purpose="definition">
		The data of the file.
		</documentation>
		</element>
		</EBMLSchema>
		</sourcecode>
		</section>

		<section anchor="ebmlschema-element"><name><tt><EBMLSchema></tt> Element</
		name>
		<t>Within an EBML Schema, the XPath <xref target="XPath"></xref> of the
		<tt><EBMLSchema></tt> element is <tt>/EBMLSchema</tt>.</t>
		<t>When used as an XML Document, the EBML Schema <bcp14>MUST</bcp14> use
		<tt><EBMLSchema></tt> as the top-level element. The
		<tt><EBMLSchema></tt> element can contain <tt><element></tt>
		subelements.</t>
		</section>

		<section anchor="ebmlschema-namespace"><name><tt><EBMLSchema></tt> Namespa
		ce</name>
		<t>The namespace URI for elements of the EBML Schema is a URN as defined by
		<xref target="RFC2141"></xref> that uses the namespace identifier 'ietf' defined
		by <xref target="RFC2648"></xref>
		and extended by <xref target="RFC3688"></xref>. This URN is <tt>urn:ietf:rfc:879
		4</tt>.</t>
		</section>

		<section anchor="ebmlschema-attributes"><name><tt><EBMLSchema></tt> Attrib
		utes</name>
		<t>Within an EBML Schema, the <tt><EBMLSchema></tt> element uses the
		following attributes to define an EBML Element:</t>

		<section anchor="doctype"><name>docType</name>
		<t>Within an EBML Schema, the XPath of the <tt>@docType</tt> attribute is
		<tt>/EBMLSchema/@docType</tt>.</t>
		<t>The docType lists the official name of the EBML Document Type that is
		defined by the EBML Schema; for example,
		<tt><EBMLSchema docType="matroska"></tt>.</t>
		<t>The <tt>docType</tt> attribute is <bcp14>REQUIRED</bcp14> within the
		<tt><EBMLSchema></tt> Element.</t>
		</section>

		<section anchor="version"><name>version</name>
		<t>Within an EBML Schema, the XPath of the <tt>@version</tt> attribute is
		<tt>/EBMLSchema/@version</tt>.</t>
		<t>The version lists a nonnegative integer that specifies the version of the
		docType documented by the EBML Schema. Unlike XML Schemas, an EBML Schema
		documents all versions of a docType's definition rather than using separate
		EBML Schemas for each version of a docType. EBML Elements may be introduced
		and deprecated by using the <tt>minver</tt> and <tt>maxver</tt> attributes of
		<tt><element></tt>.</t>
		<t>The <tt>version</tt> attribute is <bcp14>REQUIRED</bcp14> within the
		<tt><EBMLSchema></tt> Element.</t>
		</section>

		<section anchor="ebml"><name>ebml</name>
		<t>Within an EBML Schema, the XPath of the <tt>@ebml</tt> attribute is <tt>/EBML
		Schema/@ebml</tt>.</t>
		<t>The <tt>ebml</tt> attribute is a positive integer that specifies the
		version of the EBML Header (see <xref target="ebmlversion-element"></xref>)
		used by the EBML Schema. If the attribute is omitted, the EBML Header version
		is 1.</t>
		</section>
		</section>

		<section anchor="element-element"><name><tt><element></tt> Element</name>
		<t>Within an EBML Schema, the XPath of the <tt><element></tt> element is
		<tt>/EBMLSchema/element</tt>.</t>
		<t>Each <tt><element></tt> defines one EBML Element through the use of
		several attributes that are defined in
		<xref target="element-attributes"></xref>. EBML Schemas <bcp14>MAY</bcp14> conta
		in
		additional attributes to extend the semantics but <bcp14>MUST NOT</bcp14>
		conflict with the definitions of the <tt><element></tt> attributes
		defined within this document.</t>
		<t>The <tt><element></tt> nodes contain a description of the meaning and u
		se of the EBML Element stored within one or more <tt><documentation></tt>
		subelements, followed by optional <tt><implementation_note></tt> subelemen
		ts, followed by zero or one <tt><restriction></tt> subelement, followed by
		optional <tt><extension></tt> subelements. All <tt><element></tt> n
		odes <bcp14>MUST</bcp14> be subelements of the <tt><EBMLSchema></tt>.</t>
		</section>

		<section anchor="element-attributes"><name><tt><element></tt> Attributes</
		name>
		<t>Within an EBML Schema, the <tt><element></tt> uses the following
		attributes to define an EBML Element:</t>

		<section anchor="name"><name>name</name>
		<t>Within an EBML Schema, the XPath of the <tt>@name</tt> attribute is
		<tt>/EBMLSchema/element/@name</tt>.</t>
		<t>The name provides the human-readable name of the EBML Element. The value of
		the name <bcp14>MUST</bcp14> be in the form of characters "A" to
		"Z", "a" to "z", "0" to "9",
		"-", and ".". The first character of the name
		<bcp14>MUST</bcp14> be in the form of an "A" to "Z",
		"a" to "z", or "0" to "9" character.</t>
		<t>The <tt>name</tt> attribute is <bcp14>REQUIRED</bcp14>.</t>
		</section>

		<section anchor="path"><name>path</name>
		<t>Within an EBML Schema, the XPath of the <tt>@path</tt> attribute is
		<tt>/EBMLSchema/element/@path</tt>.</t>
		<t>The path defines the allowed storage locations of the EBML Element within
		an EBML Document. This path <bcp14>MUST</bcp14> be defined with the full
		hierarchy of EBML Elements separated with a <tt>\</tt>. The top EBML Element
		in the path hierarchy is the first in the value. The syntax of the
		<tt>path</tt> attribute is defined using this Augmented Backus-Naur Form
		(ABNF) <xref target="RFC5234"></xref> with the case-sensitive update
		<xref target="RFC7405"></xref> notation:</t>
		<t>The <tt>path</tt> attribute is <bcp14>REQUIRED</bcp14>.</t>

		<sourcecode type="abnf">EBMLFullPath = EBMLParentPath EBMLElement

		EBMLParentPath = PathDelimiter [EBMLParents]

		EBMLParents = 0*IntermediatePathAtom EBMLLastParent
		IntermediatePathAtom = EBMLPathAtom / GlobalPlaceholder
		EBMLLastParent = EBMLPathAtom / GlobalPlaceholder

		EBMLPathAtom = [IsRecursive] EBMLAtomName PathDelimiter
		EBMLElement = [IsRecursive] EBMLAtomName

		PathDelimiter = "\"
		IsRecursive = "+"
		EBMLAtomName = ALPHA / DIGIT 0*EBMLNameChar
		EBMLNameChar = ALPHA / DIGIT / "-" / "."

		GlobalPlaceholder = "(" GlobalParentOccurrence "\)"
		GlobalParentOccurrence = [PathMinOccurrence] "-" [PathMaxOccurrence]
		PathMinOccurrence = 1*DIGIT ; no upper limit
		PathMaxOccurrence = 1*DIGIT ; no upper limit
		</sourcecode>
		<t>The <tt>*</tt>, <tt>(</tt>, and <tt>)</tt> symbols are interpreted as defined
		in <xref target="RFC5234"></xref>.</t>
		<t>The EBMLAtomName of the EBMLElement part <bcp14>MUST</bcp14> be equal to the
		<tt>@name</tt> attribute of the EBML Schema.
		If the EBMLElement part contains an IsRecursive part, the EBML Element can occur
		within itself recursively (see <xref target="recursive"></xref>).</t>
		<t>The starting PathDelimiter of EBMLParentPath corresponds to the root of the E
		BML Document.</t>
		<t>The <tt>@path</tt> value <bcp14>MUST</bcp14> be unique within the EBML Schema
		. The <tt>@id</tt> value corresponding to this <tt>@path</tt> <bcp14>MUST NOT</b
		cp14> be defined for use within another EBML Element with the same EBMLParentPat
		h as this <tt>@path</tt>.</t>
		<t>A path with a GlobalPlaceholder as the EBMLLastParent defines a Global Elemen
		t; see <xref target="global-elements"></xref>.
		If the element has no EBMLLastParent part, or the EBMLLastParent part is not a
		GlobalPlaceholder, then the Element is not a Global Element.</t>
		<t>The GlobalParentOccurrence part is interpreted as the number of valid
		EBMLPathAtom parts that can replace the GlobalPlaceholder in the path.
		PathMinOccurrence represents the minimum number of EBMLPathAtoms required to
		replace the GlobalPlaceholder. PathMaxOccurrence represents the maximum number
		of EBMLPathAtoms possible to replace the GlobalPlaceholder.</t>
		<t>If PathMinOccurrence is not present, then that GlobalParentOccurrence has a
		PathMinOccurrence value of 0.
		If PathMaxOccurrence is not present, then there is no upper bound for the
		permitted number of EBMLPathAtoms possible to replace the GlobalPlaceholder.
		PathMaxOccurrence <bcp14>MUST NOT</bcp14> have the value 0, as it would mean
		no EBMLPathAtom can replace the GlobalPlaceholder, and the EBMLFullPath would
		be the same without that GlobalPlaceholder part.
		PathMaxOccurrence <bcp14>MUST</bcp14> be bigger than, or equal to,
		PathMinOccurrence.</t>
		<t>For example, in <tt>\a\(0-1\)global</tt>, the Element path
		<tt>\a\x\global</tt> corresponds to an EBMLPathAtom occurrence of 1. The
		Element <tt>\a\x\y\global</tt> corresponds to an EBMLPathAtom occurrence of 2,
		etc. In those cases, <tt>\a\x</tt> or <tt>\a\x\y</tt> <bcp14>MUST</bcp14> be val
		id
		paths to be able to contain the element <tt>global</tt>.</t>
		<t>Consider another EBML Path, <tt>\a\(1-\)global</tt>. There has to be at
		least one EBMLPathAtom between the <tt>\a\</tt> part and <tt>global</tt>.
		So the <tt>global</tt> EBML Element cannot be found inside the <tt>\a</tt>
		EBML Element, as it means the resulting path <tt>\a\global</tt> has no
		EBMLPathAtom between the <tt>\a\</tt> and <tt>global</tt>. However, the
		<tt>global</tt> EBML Element can be found inside the <tt>\a\b</tt> EBML
		Element, because the resulting path, <tt>\a\b\global</tt>, has one EBMLPathAtom
		between the <tt>\a\</tt> and <tt>global</tt>. Alternatively, it can be found
		inside the <tt>\a\b\c</tt> EBML Element (two EBMLPathAtom), or inside the
		<tt>\a\b\c\d</tt> EBML Element (three EBMLPathAtom), etc.</t>
		<t>Consider another EBML Path, <tt>\a\(0-1\)global</tt>. There has to be at
		most one EBMLPathAtom between the <tt>\a\</tt> part and <tt>global</tt>.
		So the <tt>global</tt> EBML Element can be found inside either the <tt>\a</tt>
		EBML Element (0 EBMLPathAtom replacing GlobalPlaceholder) or the
		<tt>\a\b</tt> EBML Element (one replacement EBMLPathAtom).
		But it cannot be found inside the <tt>\a\b\c</tt> EBML Element, because the
		resulting path, <tt>\a\b\c\global</tt>, has two EBMLPathAtom between
		<tt>\a\</tt> and <tt>global</tt>.</t>
		</section>

		<section anchor="id"><name>id</name>
		<t>Within an EBML Schema, the XPath of the <tt>@id</tt> attribute is
		<tt>/EBMLSchema/element/@id</tt>.</t>
		<t>The Element ID is encoded as a Variable-Size Integer. It is read and stored i
		n big-endian
		order. In the EBML Schema, it is expressed in
		hexadecimal notation prefixed by a 0x. To reduce the risk of false positives whi
		le parsing EBML Streams, the
		Element IDs of the Root Element and Top-Level Elements <bcp14>SHOULD</bcp14>
		be at least 4 octets in length. Element IDs defined for use at Root Level or
		directly under the Root Level <bcp14>MAY</bcp14> use shorter octet lengths to
		facilitate padding and optimize edits to EBML Documents; for instance, the
		Void Element uses an Element ID with a length of one octet to allow its usage
		in more writing and editing scenarios.</t>
		<t>The Element ID of any Element found within an EBML Document <bcp14>MUST</bcp1
		4> only match a single <tt>@path</tt> value of its corresponding EBML Schema, bu
		t a separate instance of that Element ID value defined by the EBML Schema <bcp14
		>MAY</bcp14> occur within a different <tt>@path</tt>. If more than one Element i
		s defined to use the same <tt>@id</tt> value, then the <tt>@path</tt> values of
		those Elements <bcp14>MUST NOT</bcp14> share the same EBMLParentPath. Elements <
		bcp14>MUST NOT</bcp14> be defined to use the same <tt>@id</tt> value if one of t
		heir common Parent Elements could be an Unknown-Sized Element.</t>
		<t>The <tt>id</tt> attribute is <bcp14>REQUIRED</bcp14>.</t>
		</section>

		<section anchor="minoccurs"><name>minOccurs</name>
		<t>Within an EBML Schema, the XPath of the <tt>@minOccurs</tt> attribute is
		<tt>/EBMLSchema/element/@minOccurs</tt>.</t>
		<t><tt>minOccurs</tt> is a nonnegative integer expressing the minimum permitted
		number
		of occurrences of this EBML Element within its Parent Element.</t>
		<t>Each instance of the Parent Element <bcp14>MUST</bcp14> contain at least this
		many instances of this EBML Element.
		If the EBML Element has an empty EBMLParentPath, then <tt>minOccurs</tt> refers
		to
		constraints on the occurrence of the EBML Element within the EBML Document.
		EBML Elements with <tt>minOccurs</tt> set to "1" that also have a defa
		ult
		value (see <xref target="default"></xref>) declared are not
		<bcp14>REQUIRED</bcp14> to be stored but are <bcp14>REQUIRED</bcp14> to be
		interpreted; see
		<xref target="note-on-the-use-of-default-attributes-to-define-mandatory-ebml-ele
		ments"></xref>.</t>
		<t>An EBML Element defined with a <tt>minOccurs</tt> value greater than zero is
		called
		a Mandatory EBML Element.</t>
		<t>The <tt>minOccurs</tt> attribute is <bcp14>OPTIONAL</bcp14>. If the <tt>minOc
		curs</tt>
		attribute is not present, then that EBML Element has a <tt>minOccurs</tt> value
		of
		0.</t>
		<t>The semantic meaning of <tt>minOccurs</tt> within an EBML Schema is analogous
		to the meaning of <tt>minOccurs</tt> within an XML Schema.</t>
		</section>

		<section anchor="maxoccurs"><name>maxOccurs</name>
		<t>Within an EBML Schema, the XPath of the <tt>@maxOccurs</tt> attribute is
		<tt>/EBMLSchema/element/@maxOccurs</tt>.</t>
		<t><tt>maxOccurs</tt> is a nonnegative integer expressing the maximum permitted
		number
		of occurrences of this EBML Element within its Parent Element.</t>
		<t>Each instance of the Parent Element <bcp14>MUST</bcp14> contain at most
		this many instances of this EBML Element, including the unwritten mandatory
		element with a default value; see
		<xref target="note-on-the-use-of-default-attributes-to-define-mandatory-ebml-ele
		ments"></xref>.
		If the EBML Element has an empty EBMLParentPath, then <tt>maxOccurs</tt> refers
		to
		constraints on the occurrence of the EBML Element within the EBML
		Document.</t>
		<t>The <tt>maxOccurs</tt> attribute is <bcp14>OPTIONAL</bcp14>. If the <tt>maxOc
		curs</tt>
		attribute is not present, then there is no upper bound for the permitted
		number of occurrences of this EBML Element within its Parent Element or within
		the EBML Document, depending on whether or not the EBMLParentPath of the EBML El
		ement
		is empty.</t>
		<t>The semantic meaning of <tt>maxOccurs</tt> within an EBML Schema is analogous
		to the
		meaning of <tt>maxOccurs</tt> within an XML Schema; when it is not present, it's
		similar to xml:maxOccurs="unbounded" in an XML Schema.</t>
		</section>

		<section anchor="range"><name>range</name>
		<t>Within an EBML Schema, the XPath of the <tt>@range</tt> attribute is
		<tt>/EBMLSchema/element/@range</tt>.</t>
		<t>A numerical range for EBML Elements that are of numerical types (Unsigned
		Integer, Signed Integer, Float, and Date). If specified, the value of the EBML
		Element <bcp14>MUST</bcp14> be within the defined range. See
		<xref target="expression-of-range"></xref> for rules applied to expression of ra
		nge
		values.</t>
		<t>The <tt>range</tt> attribute is <bcp14>OPTIONAL</bcp14>. If the
		<tt>range</tt> attribute is
		not present, then any value legal for the <tt>type</tt> attribute is valid.</t>

		<section anchor="expression-of-range"><name>Expression of range</name>
		<t>The <tt>range</tt> attribute <bcp14>MUST</bcp14> only be used with EBML Eleme
		nts
		that are either signed integer, unsigned integer, float, or date. The
		expression defines the upper, lower, exact, or excluded value of the EBML
		Element and optionally an upper boundary value combined with a lower
		boundary. The range expression may contain whitespace (using the ASCII 0x20
		character) for readability, but whitespace within a range expression
		<bcp14>MUST NOT</bcp14> convey meaning.</t>
		<t>To set a fixed value for the range, the value is used as the attribute
		value. For example, <tt>1234</tt> means the EBML element always has the value
		1234. The value can be prefixed with <tt>not</tt> to indicate that the fixed
		value <bcp14>MUST NOT</bcp14> be used for that Element. For example,
		<tt>not 1234</tt> means the Element can use all values of its type except 1234.<
		/t>
		<t>The <tt>></tt> sign is used for an exclusive lower boundary, and the
		<tt>>=</tt> sign is used for an inclusive lower boundary. For example,
		<tt>>3</tt> means the Element value <bcp14>MUST</bcp14> be greater than 3,
		and <tt>>=0x1p+0</tt> means the Element value <bcp14>MUST</bcp14> be
		greater than or equal to the floating value 1.0; see
		<xref target="textual-expression-of-floats"></xref>.</t>
		<t>The <tt><</tt> sign is used for an exclusive upper boundary, and the
		<tt><=</tt> sign is used for an inclusive upper boundary. For example,
		<tt><-2</tt> means the Element value <bcp14>MUST</bcp14> be less than -2,
		and <tt><=10</tt> means the Element value <bcp14>MUST</bcp14> be less than
		or equal to 10.</t>
		<t>The lower and upper bounds can be combined into an expression to form a
		closed boundary. The lower boundary comes first, followed by the upper
		boundary, separated by a comma. For example, <tt>>3,<= 20</tt> means the
		Element value <bcp14>MUST</bcp14> be greater than 3 and less than or equal to
		20.</t>
		<t>A special form of lower and upper bounds using the <tt>-</tt> separator is
		possible, meaning the Element value <bcp14>MUST</bcp14> be greater than, or equa
		l to,
		the first value and <bcp14>MUST</bcp14> be less than or equal to the
		second value. For example, <tt>1-10</tt> is equivalent to
		<tt>>=1,<=10</tt>. If the upper boundary is negative, the <tt>range</tt> a
		ttribute
		<bcp14>MUST</bcp14> only use the latter form.</t>
		</section>
		</section>

		<section anchor="length"><name>length</name>
		<t>Within an EBML Schema, the XPath of the <tt>@length</tt> attribute is
		<tt>/EBMLSchema/element/@length</tt>.</t>
		<t>The <tt>length</tt> attribute is a value to express the valid length of the E
		lement
		Data as written, measured in octets. The length provides a constraint in
		addition to the Length value of the definition of the corresponding EBML
		Element Type. This length <bcp14>MUST</bcp14> be expressed as either a
		nonnegative integer or a range (see
		<xref target="expression-of-range"></xref>) that consists of only nonnegative
		integers and valid operators.</t>
		<t>The <tt>length</tt> attribute is <bcp14>OPTIONAL</bcp14>. If the
		<tt>length</tt> attribute is
		not present for that EBML Element, then that EBML Element is only limited in
		length by the definition of the associated EBML Element Type.</t>
		</section>

		<section anchor="default"><name>default</name>
		<t>Within an EBML Schema, the XPath of the <tt>@default</tt> attribute is
		<tt>/EBMLSchema/element/@default</tt>.</t>
		<t>If an Element is mandatory (has a <tt>minOccurs</tt> value greater than zero)
		but not written within its Parent Element or stored as an Empty Element, then t
		he EBML Reader of the EBML Document <bcp14>MUST</bcp14> semantically interpret t
		he EBML Element as present with this specified default value for the EBML Elemen
		t.
		An unwritten mandatory Element with a declared default value is semantically equ
		ivalent to that Element if written with the default value stored as the Element
		Data.
		EBML Elements that are Master Elements <bcp14>MUST NOT</bcp14> declare a default
		value.
		EBML Elements with a <tt>minOccurs</tt> value greater than 1 <bcp14>MUST NOT</bc
		p14> declare a default value.</t>
		<t>The default attribute is <bcp14>OPTIONAL</bcp14>.</t>
		</section>

		<section anchor="type"><name>type</name>
		<t>Within an EBML Schema, the XPath of the <tt>@type</tt> attribute is
		<tt>/EBMLSchema/element/@type</tt>.</t>
		<t>The type <bcp14>MUST</bcp14> be set to one of the following values:
		<tt>integer</tt> (signed integer), <tt>uinteger</tt> (unsigned integer),
		<tt>float</tt>, <tt>string</tt>, <tt>date</tt>, <tt>utf-8</tt>,
		<tt>master</tt>, or <tt>binary</tt>. The content of each type is defined
		in <xref target="ebml-element-types"></xref>.</t>
		<t>The <tt>type</tt> attribute is <bcp14>REQUIRED</bcp14>.</t>
		</section>

		<section anchor="unknownsizeallowed"><name>unknownsizeallowed</name>
		<t>Within an EBML Schema, the XPath of the <tt>@unknownsizeallowed</tt>
		attribute is <tt>/EBMLSchema/element/@unknownsizeallowed</tt>.</t>
		<t>This attribute is a boolean to express whether an EBML Element is permitted t
		o
		be an Unknown-Sized Element (having all VINT_DATA bits of Element Data Size set
		to 1). EBML Elements that are not Master Elements <bcp14>MUST NOT</bcp14> set
		<tt>unknownsizeallowed</tt> to true. An EBML Element that is defined with an
		<tt>unknownsizeallowed</tt> attribute set to 1 <bcp14>MUST</bcp14> also have the
		<tt>unknownsizeallowed</tt> attribute of its Parent Element set to 1.</t>
		<t>An EBML Element with the <tt>unknownsizeallowed</tt> attribute set to 1
		<bcp14>MUST NOT</bcp14> have its <tt>recursive</tt> attribute set to 1.</t>
		<t>The <tt>unknownsizeallowed</tt> attribute is <bcp14>OPTIONAL</bcp14>. If the
		<tt>unknownsizeallowed</tt> attribute is not used, then that EBML Element is not
		allowed to use an unknown Element Data Size.</t>
		</section>

		<section anchor="recursive"><name>recursive</name>
		<t>Within an EBML Schema, the XPath of the <tt>@recursive</tt> attribute is
		<tt>/EBMLSchema/element/@recursive</tt>.</t>
		<t>This attribute is a boolean to express whether an EBML Element is permitted t
		o
		be stored recursively. If it is allowed, the EBML Element <bcp14>MAY</bcp14> be
		stored within another EBML Element that has the same Element ID, which itself
		can be stored in an EBML Element that has the same Element ID, and so on. EBML
		Elements that are not Master Elements <bcp14>MUST NOT</bcp14> set recursive to
		true.</t>
		<t>If the EBMLElement part of the <tt>@path</tt> contains an IsRecursive part,
		then the <tt>recursive</tt> value <bcp14>MUST</bcp14> be true; otherwise, it
		<bcp14>MUST</bcp14> be false.</t>
		<t>An EBML Element with the <tt>recursive</tt> attribute set to 1 <bcp14>MUST NO
		T</bcp14>
		have its <tt>unknownsizeallowed</tt> attribute set to 1.</t>
		<t>The <tt>recursive</tt> attribute is <bcp14>OPTIONAL</bcp14>. If the <tt>recur
		sive</tt>
		attribute is not present, then the EBML Element <bcp14>MUST NOT</bcp14> be
		used recursively.</t>
		</section>

		<section anchor="recurring"><name>recurring</name>
		<t>Within an EBML Schema, the XPath of the <tt>@recurring</tt> attribute is
		<tt>/EBMLSchema/element/@recurring</tt>.</t>
		<t>This attribute is a boolean to express whether or not an EBML Element is defi
		ned as an
		Identically Recurring Element; see
		<xref target="identically-recurring-elements"></xref>.</t>
		<t>The <tt>recurring</tt> attribute is <bcp14>OPTIONAL</bcp14>. If the <tt>recur
		ring</tt>
		attribute is not present, then the EBML Element is not an Identically
		Recurring Element.</t>
		</section>

		<section anchor="minver"><name>minver</name>
		<t>Within an EBML Schema, the XPath of the <tt>@minver</tt> attribute is
		<tt>/EBMLSchema/element/@minver</tt>.</t>
		<t>The <tt>minver</tt> (minimum version) attribute stores a nonnegative integer
		that
		represents the first version of the docType to support the EBML Element.</t>
		<t>The <tt>minver</tt> attribute is <bcp14>OPTIONAL</bcp14>. If the <tt>minver</
		tt>
		attribute is not present, then the EBML Element has a minimum version of
		"1".</t>
		</section>

		<section anchor="maxver"><name>maxver</name>
		<t>Within an EBML Schema, the XPath of the <tt>@maxver</tt> attribute is
		<tt>/EBMLSchema/element/@maxver</tt>.</t>
		<t>The <tt>maxver</tt> (maximum version) attribute stores a nonnegative integer
		that
		represents the last or most recent version of the docType to support the
		element. <tt>maxver</tt> <bcp14>MUST</bcp14> be greater than or equal to <tt>min
		ver</tt>.</t>
		<t>The <tt>maxver</tt> attribute is <bcp14>OPTIONAL</bcp14>. If the <tt>maxver</
		tt> attribute is
		not present, then the EBML Element has a maximum version equal to the value
		stored in the <tt>version</tt> attribute of <tt><EBMLSchema></tt>.</t>
		</section>
		</section>

		<section anchor="documentation-element"><name><tt><documentation></tt> Ele
		ment</name>
		<t>Within an EBML Schema, the XPaths of the <tt><documentation></tt>
		elements are <tt>/EBMLSchema/element/documentation</tt> and <tt>/EBMLSchema/elem
		ent/restriction/enum/documentation</tt>.</t>
		<t>The <tt><documentation></tt> element provides additional information
		about EBML Elements or enumeration values. Within the <tt><documentation><
		/tt> element, the
		following XHTML <xref target="XHTML"></xref> elements <bcp14>MAY</bcp14> be
		used: <tt><a></tt>, <tt><br></tt>, and <tt><strong></tt>.</t>
		</section>

		<section anchor="documentation-attributes"><name><tt><documentation></tt>
		Attributes</name>

		<section anchor="lang"><name>lang</name>
		<t>Within an EBML Schema, the XPath of the <tt>@lang</tt> attribute is
		<tt>/EBMLSchema/element/documentation/@lang</tt>.</t>
		<t>The <tt>lang</tt> attribute is set to the value from <xref target="RFC5646"><
		/xref> of
		the language of the element's documentation.</t>
		<t>The <tt>lang</tt> attribute is <bcp14>OPTIONAL</bcp14>.</t>
		</section>

		<section anchor="purpose"><name>purpose</name>
		<t>Within an EBML Schema, the XPath of the <tt>@purpose</tt> attribute is
		<tt>/EBMLSchema/element/documentation/@purpose</tt>.</t>
		<t>A <tt>purpose</tt> attribute distinguishes the meaning of the documentation.
		Values
		for the <tt><documentation></tt> subelement's <tt>purpose</tt> attribute
		<bcp14>MUST</bcp14> include one of the values listed in
		<xref target="tablePurposeDefinitions"></xref>.</t>
		<table anchor="tablePurposeDefinitions"><name>Definitions of the permitted
		values for the <tt>purpose</tt> attribute of the documentation Element</name>
		<thead>
		<tr>
		<th align="left">value of <tt>purpose</tt> attribute</th>
		<th align="left">definition</th>
		</tr>
		</thead>

		<tbody>
		<tr>
		<td align="left">definition</td>
		<td align="left">A "definition" is recommended for every defined EBML
		Element. This documentation explains the semantic meaning of the EBML Element.</
		td>
		</tr>

		<tr>
		<td align="left">rationale</td>
		<td align="left">An explanation about the reason or catalyst for the definition
		of the Element.</td>
		</tr>

		<tr>
		<td align="left">usage notes</td>
		<td align="left">Recommended practices or guidelines for both reading, writing,
		or interpreting the Element.</td>
		</tr>

		<tr>
		<td align="left">references</td>
		<td align="left">Informational references to support the contextualization and u
		nderstanding of the value of the Element.</td>
		</tr>
		</tbody>
		</table><t>The <tt>purpose</tt> attribute is <bcp14>REQUIRED</bcp14>.</t>
		</section>
		</section>

		<section anchor="implementation-note-element"><name><tt><implementation_note&
		gt;</tt> Element</name>
		<t>Within an EBML Schema, the XPath of the <tt><implementation_note></tt>
		element is <tt>/EBMLSchema/element/implementation_note</tt>.</t>
		<t>In some cases within an EBML Document Type, the attributes of the
		<tt><element></tt> element are not sufficient to clearly communicate how
		the defined EBML Element is intended to be implemented.
		For instance, one EBML Element might only be mandatory if another EBML Element
		is present. As another example, the default value of an EBML Element might
		be derived from a related Element's content. In these cases where the Element's
		definition is conditional or advanced implementation notes are needed, one or ma
		ny
		<tt><implementation_note></tt> elements can be used to store that
		information.
		The <tt><implementation_note></tt> refers to a specific attribute of the
		parent <tt><element></tt> as expressed by the <tt>note_attribute</tt>
		attribute (see <xref target="note-attribute"></xref>).</t>
		</section>

		<section anchor="implementation-note-attributes"><name><tt><implementation_no
		te></tt> Attributes</name>

		<section anchor="note-attribute"><name>note_attribute</name>
		<t>Within an EBML Schema, the XPath of the <tt>@note_attribute</tt> attribute
		is <tt>/EBMLSchema/element/implementation_note/@note_attribute</tt>.</t>
		<t>The <tt>note_attribute</tt> attribute references which of the attributes of t
		he
		<tt><element></tt> the <tt><implementation_note></tt> relates to.
		The <tt>note_attribute</tt> attribute <bcp14>MUST</bcp14> be set to one of the
		following values (corresponding to that attribute of the parent
		<tt><element></tt>): <tt>minOccurs</tt>, <tt>maxOccurs</tt>,
		<tt>range</tt>, <tt>length</tt>, <tt>default</tt>, <tt>minver</tt>, or
		<tt>maxver</tt>. The <tt><implementation_note></tt> <bcp14>SHALL</bcp14>
		supersede the parent <tt><element></tt>'s attribute that is named in the
		<tt>note_attribute</tt> attribute.
		An <tt><element></tt> <bcp14>SHALL NOT</bcp14> have more than one <tt><
		implementation_note></tt> of the same <tt>note_attribute</tt>.</t>
		<t>The <tt>note_attribute</tt> attribute is <bcp14>REQUIRED</bcp14>.</t>
		</section>

		<section anchor="implementation-note-example"><name><tt><implementation_note&
		gt;</tt> Example</name>
		<t>The following fragment of an EBML Schema demonstrates how an
		<tt><implementation_note></tt> is used. In this case, an EBML Schema
		documents a list of items that are described with an optional cost. The
		Currency Element uses an <tt><implementation_note></tt> to say that the
		Currency Element is <bcp14>REQUIRED</bcp14> if the Cost Element is set,
		otherwise not.</t>

		<sourcecode type="xml"><element name="Items" path="\Items&quot
		; id="0x4025" type="master"
		minOccurs="1" maxOccurs="1">
		<documentation lang="en" purpose="definition">
		A set of items.
		</documentation>
		</element>
		<element name="Item" path="\Items\Item" id="0x4026&q
		uot;
		type="master">
		<documentation lang="en" purpose="definition">
		An item.
		</documentation>
		</element>
		<element name="Cost" path="\Items\Item\Cost" id="0x4
		024"
		type="float" maxOccurs="1">
		<documentation lang="en" purpose="definition">
		The cost of the item, if any.
		</documentation>
		</element>
		<element name="Currency" path="\Items\Item\Currency" id=&
		quot;0x403F"
		type="string" maxOccurs="1">
		<documentation lang="en" purpose="definition">
		The currency of the item's cost.
		</documentation>
		<implementation_note note_attribute="minOccurs">
		Currency MUST be set (minOccurs=1) if the associated Item stores
		a Cost, else Currency MAY be unset (minOccurs=0).
		</implementation_note>
		</element>
		</sourcecode>
		</section>
		</section>

		<section anchor="restriction-element"><name><tt><restriction></tt> Element
		</name>
		<t>Within an EBML Schema, the XPath of the <tt><restriction></tt>
		element is <tt>/EBMLSchema/element/restriction</tt>.</t>
		<t>The <tt><restriction></tt> element provides information about
		restrictions to the allowable values for the EBML Element, which are listed in
		<tt><enum></tt> elements.</t>
		</section>

		<section anchor="enum-element"><name><tt><enum></tt> Element</name>
		<t>Within an EBML Schema, the XPath of the <tt><enum></tt> element is
		<tt>/EBMLSchema/element/restriction/enum</tt>.</t>
		<t>The <tt><enum></tt> element stores a list of values allowed for
		storage in the EBML Element. The values <bcp14>MUST</bcp14> match the type of
		the EBML Element (for example, <tt><enum value="Yes"></tt>
		cannot be a valid value for an EBML Element that is defined as an unsigned
		integer). An <tt><enum></tt> element <bcp14>MAY</bcp14> also store
		<tt><documentation></tt> elements to further describe the
		<tt><enum></tt>.</t>
		</section>

		<section anchor="enum-attributes"><name><tt><enum></tt> Attributes</name>

		<section anchor="label"><name>label</name>
		<t>Within an EBML Schema, the XPath of the <tt>@label</tt> attribute is
		<tt>/EBMLSchema/element/restriction/enum/@label</tt>.</t>
		<t>The label provides a concise expression for human consumption that
		describes what the value of <tt><enum></tt> represents.</t>
		<t>The <tt>label</tt> attribute is <bcp14>OPTIONAL</bcp14>.</t>
		</section>

		<section anchor="value"><name>value</name>
		<t>Within an EBML Schema, the XPath of the <tt>@value</tt> attribute is
		<tt>/EBMLSchema/element/restriction/enum/@value</tt>.</t>
		<t>The value represents data that <bcp14>MAY</bcp14> be stored within the EBML E
		lement.</t>
		<t>The <tt>value</tt> attribute is <bcp14>REQUIRED</bcp14>.</t>
		</section>
		</section>

		<section anchor="extension-element"><name><tt><extension></tt> Element</na
		me>
		<t>Within an EBML Schema, the XPath of the <tt><extension></tt>
		element is <tt>/EBMLSchema/element/extension</tt>.</t>
		<t>The <tt><extension></tt> element provides an unconstrained element to
		contain information about the associated EBML <tt><element></tt>, which
		is undefined by this document but <bcp14>MAY</bcp14> be defined by the
		associated EBML Document Type. The <tt><extension></tt> element
		<bcp14>MUST</bcp14> contain a <tt>type</tt> attribute and also
		<bcp14>MAY</bcp14> contain any other attribute or subelement as long as the
		EBML Schema remains as a well-formed XML Document. All
		<tt><extension></tt> elements <bcp14>MUST</bcp14> be subelements of the
		<tt><element></tt>.</t>
		</section>

		<section anchor="extension-attributes"><name><tt><extension></tt> Attribut
		es</name>

		<section anchor="type-1"><name>type</name>
		<t>Within an EBML Schema, the XPath of the <tt>@type</tt> attribute is
		<tt>/EBMLSchema/element/extension/@type</tt>.</t>
		<t>The <tt>type</tt> attribute should reference a name or identifier of the
		project or authority associated with the contents of the
		<tt><extension></tt> element.</t>
		<t>The <tt>type</tt> attribute is <bcp14>REQUIRED</bcp14>.</t>
		</section>
		</section>

		<section anchor="xml-schema-for-ebml-schema"><name>XML Schema for EBML Schema</n
		ame>
		<t>The following provides an XML Schema <xref target="XML-SCHEMA"></xref> for
		facilitating verification of an EBML Schema described in
		<xref target="ebml-schema"></xref>.</t>

		<sourcecode type="xml"><?xml version="1.0" encoding="UTF-8&quo
		t;?>
		<xs:schema xmlns="urn:ietf:rfc:8794"
		targetNamespace="urn:ietf:rfc:8794"
		xmlns:xs="http://www.w3.org/2001/XMLSchema"
		xmlns:xhtml="http://www.w3.org/1999/xhtml"
		elementFormDefault="qualified" version="01">

		<!-- for HTML in comments -->
		<xs:import namespace="http://www.w3.org/1999/xhtml"
		schemaLocation="http://www.w3.org/MarkUp/SCHEMA/xhtml11.xsd"/>

		<xs:element name="EBMLSchema" type="EBMLSchemaType"/&gt
		;

		<xs:complexType name="EBMLSchemaType">
		<xs:sequence>
		<xs:element name="element" type="elementType"
		minOccurs="0" maxOccurs="unbounded"/>
		</xs:sequence>
		<xs:attribute name="docType" use="required"/>
		<xs:attribute name="version" use="required" type=&quo
		t;xs:integer"/>
		<xs:attribute name="ebml" type="xs:positiveInteger"
		default="1"/>
		</xs:complexType>

		<xs:complexType name="elementType">
		<xs:sequence>
		<xs:element name="documentation" type="documentationType
		"
		minOccurs="0" maxOccurs="unbounded"/>
		<xs:element name="implementation_note" type="noteType&qu
		ot;
		minOccurs="0" maxOccurs="unbounded"/>
		<xs:element name="restriction" type="restrictionType&quo
		t;
		minOccurs="0" maxOccurs="1"/>
		<xs:element name="extension" type="extensionType"
		minOccurs="0" maxOccurs="unbounded"/>
		</xs:sequence>
		<xs:attribute name="name" use="required">
		<xs:simpleType>
		<xs:restriction base="xs:string">
		<xs:pattern value="[0-9A-Za-z.-]([0-9A-Za-z.-])*"/>
		</xs:restriction>
		</xs:simpleType>
		</xs:attribute>
		<xs:attribute name="path" use="required">
		<!-- <xs:simpleType>
		<xs:restriction base="xs:integer">
		<xs:pattern value="[0-9]\[0-9]*()"/>
		</xs:restriction>
		</xs:simpleType> -->
		</xs:attribute>
		<xs:attribute name="id" use="required">
		<xs:simpleType>
		<xs:restriction base="xs:string">
		<xs:pattern value="0x([0-9A-F][0-9A-F])+"/>
		</xs:restriction>
		</xs:simpleType>
		</xs:attribute>
		<xs:attribute name="minOccurs" default="0">
		<xs:simpleType>
		<xs:restriction base="xs:integer">
		<xs:minInclusive value="0"/>
		</xs:restriction>
		</xs:simpleType>
		</xs:attribute>
		<xs:attribute name="maxOccurs" default="1">
		<xs:simpleType>
		<xs:restriction base="xs:integer">
		<xs:minInclusive value="0"/>
		</xs:restriction>
		</xs:simpleType>
		</xs:attribute>
		<xs:attribute name="range"/>
		<xs:attribute name="length"/>
		<xs:attribute name="default"/>
		<xs:attribute name="type" use="required">
		<xs:simpleType>
		<xs:restriction base="xs:string">
		<xs:enumeration value="integer"/>
		<xs:enumeration value="uinteger"/>
		<xs:enumeration value="float"/>
		<xs:enumeration value="string"/>
		<xs:enumeration value="date"/>
		<xs:enumeration value="utf-8"/>
		<xs:enumeration value="master"/>
		<xs:enumeration value="binary"/>
		</xs:restriction>
		</xs:simpleType>
		</xs:attribute>
		<xs:attribute name="unknownsizeallowed" type="xs:boolean&q
		uot;
		default="false"/>
		<xs:attribute name="recursive" type="xs:boolean"
		default="false"/>
		<xs:attribute name="recurring" type="xs:boolean"
		default="false"/>
		<xs:attribute name="minver" default="1">
		<xs:simpleType>
		<xs:restriction base="xs:integer">
		<xs:minInclusive value="0"/>
		</xs:restriction>
		</xs:simpleType>
		</xs:attribute>
		<xs:attribute name="maxver">
		<xs:simpleType>
		<xs:restriction base="xs:integer">
		<xs:minInclusive value="0"/>
		</xs:restriction>
		</xs:simpleType>
		</xs:attribute>
		</xs:complexType>

		<xs:complexType name="restrictionType">
		<xs:sequence>
		<xs:element name="enum" type="enumType"
		minOccurs="0" maxOccurs="unbounded"/>
		</xs:sequence>
		</xs:complexType>

		<xs:complexType name="extensionType">
		<xs:sequence>
		<xs:any processContents="skip"
		minOccurs="0" maxOccurs="unbounded"/>
		</xs:sequence>
		<xs:attribute name="type" use="required"/>
		<xs:anyAttribute processContents="skip"/>
		</xs:complexType>

		<xs:complexType name="enumType">
		<xs:sequence>
		<xs:element name="documentation" type="documentationType
		"
		minOccurs="0" maxOccurs="unbounded"/>
		</xs:sequence>
		<xs:attribute name="label"/>
		<xs:attribute name="value" use="required"/>
		</xs:complexType>

		<xs:complexType name="documentationType" mixed="true"&g
		t;
		<xs:sequence>
		<xs:element name="a" type="xhtml:xhtml.a.type"
		minOccurs="0" maxOccurs="unbounded"/>
		<xs:element name="br" type="xhtml:xhtml.br.type&quot
		;
		minOccurs="0" maxOccurs="unbounded"/>
		<xs:element name="strong" type="xhtml:xhtml.strong.type&
		quot;
		minOccurs="0" maxOccurs="unbounded"/>
		</xs:sequence>
		<xs:attribute name="lang"/>
		<xs:attribute name="purpose" use="required">
		<xs:simpleType>
		<xs:restriction base="xs:string">
		<xs:enumeration value="definition"/>
		<xs:enumeration value="rationale"/>
		<xs:enumeration value="references"/>
		<xs:enumeration value="usage notes"/>
		</xs:restriction>
		</xs:simpleType>
		</xs:attribute>
		</xs:complexType>

		<xs:complexType name="noteType">
		<xs:simpleContent>
		<xs:extension base="xs:string">
		<xs:attribute name="note_attribute" use="required&quot
		;>
		<xs:simpleType>
		<xs:restriction base="xs:string">
		<xs:enumeration value="minOccurs"/>
		<xs:enumeration value="maxOccurs"/>
		<xs:enumeration value="range"/>
		<xs:enumeration value="length"/>
		<xs:enumeration value="default"/>
		<xs:enumeration value="minver"/>
		<xs:enumeration value="maxver"/>
		</xs:restriction>
		</xs:simpleType>
		</xs:attribute>
		</xs:extension>
		</xs:simpleContent>
		</xs:complexType>
		</xs:schema>
		</sourcecode>
		</section>

		<section anchor="identically-recurring-elements"><name>Identically Recurring Ele
		ments</name>
		<t>An Identically Recurring Element is an EBML Element that <bcp14>MAY</bcp14>
		occur within its Parent Element more than once, but each recurrence of it
		within that Parent Element <bcp14>MUST</bcp14> be identical both in storage
		and semantics. Identically Recurring Elements are permitted to be stored
		multiple times within the same Parent Element in order to increase data
		resilience and optimize the use of EBML in transmission. For instance, a
		pertinent Top-Level Element could be periodically resent within a datastream
		so that an EBML Reader that starts reading the stream from the middle could
		better interpret the contents. Identically Recurring Elements
		<bcp14>SHOULD</bcp14> include a CRC-32 Element as a Child Element; this is
		especially recommended when EBML is used for long-term storage or
		transmission. If a Parent Element contains more than one copy of an
		Identically Recurring Element that includes a CRC-32 Element as a Child
		Element, then the first instance of the Identically Recurring Element with a
		valid CRC-32 value should be used for interpretation. If a Parent Element
		contains more than one copy of an Identically Recurring Element that does not
		contain a CRC-32 Element, or if CRC-32 Elements are present but none are valid,
		then the first instance of the Identically Recurring Element should be used
		for interpretation.</t>
		</section>

		<section anchor="textual-expression-of-floats"><name>Textual expression of float
		s</name>
		<t>When a float value is represented textually in an EBML Schema, such as
		within a default or range value, the float values <bcp14>MUST</bcp14> be
		expressed as Hexadecimal Floating-Point Constants as defined in the C11
		standard <xref target="ISO9899"></xref> (see Section 6.4.4.2 on Floating
		Constants). <xref target="tableFloatExamples"></xref> provides examples of
		expressions of float ranges.</t>
		<table anchor="tableFloatExamples"><name>Example of Floating-Point values and
		ranges as decimal and Hexadecimal Floating-Point Constants</name>
		<thead>
		<tr>
		<th align="left">as decimal</th>
		<th align="left">as Hexadecimal Floating-Point Constants</th>
		</tr>
		</thead>

		<tbody>
		<tr>
		<td align="left">0.0</td>
		<td align="left"><tt>0x0p+1</tt></td>
		</tr>

		<tr>
		<td align="left">0.0-1.0</td>
		<td align="left"><tt>0x0p+1-0x1p+0</tt></td>
		</tr>

		<tr>
		<td align="left">1.0-256.0</td>
		<td align="left"><tt>0x1p+0-0x1p+8</tt></td>
		</tr>

		<tr>
		<td align="left">0.857421875</td>
		<td align="left"><tt>0x1.b7p-1</tt></td>
		</tr>

		<tr>
		<td align="left">-1.0--0.857421875</td>
		<td align="left"><tt>-0x1p+0--0x1.b7p-1</tt></td>
		</tr>
		</tbody>
		</table><t>Within an expression of a float range, as in an integer range, the
		- (hyphen) character is the separator between the minimum and maximum values
		permitted by the range. Hexadecimal Floating-Point Constants also use a -
		(hyphen) when indicating a negative binary power. Within a float range, when a
		- (hyphen) is immediately preceded by a letter p, then the - (hyphen) is a
		part of the Hexadecimal Floating-Point Constant that notes negative binary
		power. Within a float range, when a - (hyphen) is not immediately preceded by
		a letter p, then the - (hyphen) represents the separator between the minimum
		and maximum values permitted by the range.</t>
		</section>

		<section anchor="note-on-the-use-of-default-attributes-to-define-mandatory-ebml-
		elements"><name>Note on the use of default attributes to define Mandatory EBML E
		lements</name>
		<t>If a Mandatory EBML Element has a default value declared by an EBML Schema
		and the value of the EBML Element is equal to the declared default value, then
		that EBML Element is not required to be present within the EBML Document if
		its Parent Element is present. In this case, the default value of the
		Mandatory EBML Element <bcp14>MUST</bcp14> be read by the EBML Reader,
		although the EBML Element is not present within its Parent Element.</t>
		<t>If a Mandatory EBML Element has no default value declared by an EBML Schema
		and its Parent Element is present, then the EBML Element <bcp14>MUST</bcp14>
		be present, as well. If a Mandatory EBML Element has a default value declared
		by an EBML Schema, and its Parent Element is present, and the value of the EBML
		Element is NOT equal to the declared default value, then the EBML Element
		<bcp14>MUST</bcp14> be present.</t>
		<t><xref target="tableVintRequirements"></xref> clarifies whether a Mandatory
		EBML Element <bcp14>MUST</bcp14> be written, according to whether the default va
		lue
		is declared, the value of the EBML Element is equal to the declared default
		value, and/or the Parent Element is used.</t>
		<table anchor="tableVintRequirements"><name>Demonstration of the conditional
		requirements of VINT Storage</name>
		<thead>
		<tr>
		<th align="center">Is the default value declared?</th>
		<th align="center">Is the value equal to default?</th>
		<th align="center">Is the Parent Element present?</th>
		<th align="center">Then is storing the EBML Element <bcp14>REQUIRED</bcp14>?</th
		>
		</tr>
		</thead>

		<tbody>
		<tr>
		<td align="center">Yes</td>
		<td align="center">Yes</td>
		<td align="center">Yes</td>
		<td align="center">No</td>
		</tr>

		<tr>
		<td align="center">Yes</td>
		<td align="center">Yes</td>
		<td align="center">No</td>
		<td align="center">No</td>
		</tr>

		<tr>
		<td align="center">Yes</td>
		<td align="center">No</td>
		<td align="center">Yes</td>
		<td align="center">Yes</td>
		</tr>

		<tr>
		<td align="center">Yes</td>
		<td align="center">No</td>
		<td align="center">No</td>
		<td align="center">No</td>
		</tr>

		<tr>
		<td align="center">No</td>
		<td align="center">n/a</td>
		<td align="center">Yes</td>
		<td align="center">Yes</td>
		</tr>

		<tr>
		<td align="center">No</td>
		<td align="center">n/a</td>
		<td align="center">No</td>
		<td align="center">No</td>
		</tr>
		</tbody>
		</table></section>
		</section>

		<section anchor="ebml-header-elements"><name>EBML Header Elements</name>
		<t>This document contains definitions of all EBML Elements of the EBML Header.</
		t>

		<section anchor="ebml-element"><name>EBML Element</name>

		<dl>
		<dt>name:</dt>
		<dd>EBML</dd>
		<dt>path:</dt>
		<dd><tt>\EBML</tt></dd>
		<dt>id:</dt>
		<dd>0x1A45DFA3</dd>
		<dt>minOccurs:</dt>
		<dd>1</dd>
		<dt>maxOccurs:</dt>
		<dd>1</dd>
		<dt>type:</dt>
		<dd>Master Element</dd>
		<dt>description:</dt>
		<dd>Set the EBML characteristics of the data to follow. Each EBML Document has
		to start with this.</dd>
		</dl>
		</section>

		<section anchor="ebmlversion-element"><name>EBMLVersion Element</name>

		<dl>
		<dt>name:</dt>
		<dd>EBMLVersion</dd>
		<dt>path:</dt>
		<dd><tt>\EBML\EBMLVersion</tt></dd>
		<dt>id:</dt>
		<dd>0x4286</dd>
		<dt>minOccurs:</dt>
		<dd>1</dd>
		<dt>maxOccurs:</dt>
		<dd>1</dd>
		<dt>range:</dt>
		<dd>not 0</dd>
		<dt>default:</dt>
		<dd>1</dd>
		<dt>type:</dt>
		<dd>Unsigned Integer</dd>
		<dt>description:</dt>
		<dd>The version of EBML specifications used to create the EBML Document. The
		version of EBML defined in this document is 1, so EBMLVersion
		<bcp14>SHOULD</bcp14> be 1.</dd>
		</dl>
		</section>

		<section anchor="ebmlreadversion-element"><name>EBMLReadVersion Element</name>

		<dl>
		<dt>name:</dt>
		<dd>EBMLReadVersion</dd>
		<dt>path:</dt>
		<dd><tt>\EBML\EBMLReadVersion</tt></dd>
		<dt>id:</dt>
		<dd>0x42F7</dd>
		<dt>minOccurs:</dt>
		<dd>1</dd>
		<dt>maxOccurs:</dt>
		<dd>1</dd>
		<dt>range:</dt>
		<dd>1</dd>
		<dt>default:</dt>
		<dd>1</dd>
		<dt>type:</dt>
		<dd>Unsigned Integer</dd>
		<dt>description:</dt>
		<dd>The minimum EBML version an EBML Reader has to support to read this EBML
		Document. The EBMLReadVersion Element <bcp14>MUST</bcp14> be less than or equal
		to EBMLVersion.</dd>
		</dl>
		</section>

		<section anchor="ebmlmaxidlength-element"><name>EBMLMaxIDLength Element</name>

		<dl>
		<dt>name:</dt>
		<dd>EBMLMaxIDLength</dd>
		<dt>path:</dt>
		<dd><tt>\EBML\EBMLMaxIDLength</tt></dd>
		<dt>id:</dt>
		<dd>0x42F2</dd>
		<dt>minOccurs:</dt>
		<dd>1</dd>
		<dt>maxOccurs:</dt>
		<dd>1</dd>
		<dt>range:</dt>
		<dd>>=4</dd>
		<dt>default:</dt>
		<dd>4</dd>
		<dt>type:</dt>
		<dd>Unsigned Integer</dd>
		<dt>description:</dt>
		<dd>The EBMLMaxIDLength Element stores the maximum permitted length in octets
		of the Element IDs to be found within the EBML Body. An EBMLMaxIDLength Element
		value of four
		is <bcp14>RECOMMENDED</bcp14>, though larger values are allowed.</dd>
		</dl>
		</section>

		<section anchor="ebmlmaxsizelength-element"><name>EBMLMaxSizeLength Element</nam
		e>

		<dl>
		<dt>name:</dt>
		<dd>EBMLMaxSizeLength</dd>
		<dt>path:</dt>
		<dd><tt>\EBML\EBMLMaxSizeLength</tt></dd>
		<dt>id:</dt>
		<dd>0x42F3</dd>
		<dt>minOccurs:</dt>
		<dd>1</dd>
		<dt>maxOccurs:</dt>
		<dd>1</dd>
		<dt>range:</dt>
		<dd>not 0</dd>
		<dt>default:</dt>
		<dd>8</dd>
		<dt>type:</dt>
		<dd>Unsigned Integer</dd>
		<dt>description:</dt>
		<dd>The EBMLMaxSizeLength Element stores the maximum permitted length in
		octets of the expressions of all Element Data Sizes to be found within the EBML
		Body. The
		EBMLMaxSizeLength Element documents an upper bound for the <tt>length</tt> of
		all Element Data Size expressions within the EBML Body and not an upper bound
		for the <tt>value</tt> of all Element Data Size expressions
		within the EBML Body. EBML Elements that have an Element Data Size expression th
		at is larger in octets
		than what is expressed by EBMLMaxSizeLength Element are invalid.</dd>
		</dl>
		</section>

		<section anchor="doctype-element"><name>DocType Element</name>

		<dl>
		<dt>name:</dt>
		<dd>DocType</dd>
		<dt>path:</dt>
		<dd><tt>\EBML\DocType</tt></dd>
		<dt>id:</dt>
		<dd>0x4282</dd>
		<dt>minOccurs:</dt>
		<dd>1</dd>
		<dt>maxOccurs:</dt>
		<dd>1</dd>
		<dt>length:</dt>
		<dd>>0</dd>
		<dt>type:</dt>
		<dd>String</dd>
		<dt>description:</dt>
		<dd>A string that describes and identifies the content of the EBML Body that
		follows this EBML Header.</dd>
		</dl>
		</section>

		<section anchor="doctypeversion-element"><name>DocTypeVersion Element</name>

		<dl>
		<dt>name:</dt>
		<dd>DocTypeVersion</dd>
		<dt>path:</dt>
		<dd><tt>\EBML\DocTypeVersion</tt></dd>
		<dt>id:</dt>
		<dd>0x4287</dd>
		<dt>minOccurs:</dt>
		<dd>1</dd>
		<dt>maxOccurs:</dt>
		<dd>1</dd>
		<dt>range:</dt>
		<dd>not 0</dd>
		<dt>default:</dt>
		<dd>1</dd>
		<dt>type:</dt>
		<dd>Unsigned Integer</dd>
		<dt>description:</dt>
		<dd>The version of DocType interpreter used to create the EBML Document.</dd>
		</dl>
		</section>

		<section anchor="doctypereadversion-element"><name>DocTypeReadVersion Element</n
		ame>

		<dl>
		<dt>name:</dt>
		<dd>DocTypeReadVersion</dd>
		<dt>path:</dt>
		<dd><tt>\EBML\DocTypeReadVersion</tt></dd>
		<dt>id:</dt>
		<dd>0x4285</dd>
		<dt>minOccurs:</dt>
		<dd>1</dd>
		<dt>maxOccurs:</dt>
		<dd>1</dd>
		<dt>range:</dt>
		<dd>not 0</dd>
		<dt>default:</dt>
		<dd>1</dd>
		<dt>type:</dt>
		<dd>Unsigned Integer</dd>
		<dt>description:</dt>
		<dd>The minimum DocType version an EBML Reader has to support to read this
		EBML Document. The value of the DocTypeReadVersion Element <bcp14>MUST</bcp14>
		be less than or equal to the value of the DocTypeVersion Element.</dd>
		</dl>
		</section>

		<section anchor="doctypeextension-element"><name>DocTypeExtension Element</name>

		<dl>
		<dt>name:</dt>
		<dd>DocTypeExtension</dd>
		<dt>path:</dt>
		<dd><tt>\EBML\DocTypeExtension</tt></dd>
		<dt>id:</dt>
		<dd>0x4281</dd>
		<dt>minOccurs:</dt>
		<dd>0</dd>
		<dt>type:</dt>
		<dd>Master Element</dd>
		<dt>description:</dt>
		<dd>A DocTypeExtension adds extra Elements to the main DocType+DocTypeVersion
		tuple it's attached to. An EBML Reader <bcp14>MAY</bcp14> know these extra Eleme
		nts and how
		to use them. A DocTypeExtension <bcp14>MAY</bcp14> be used to iterate between
		experimental Elements before they are integrated into a regular
		DocTypeVersion. Reading one DocTypeExtension version of a
		DocType+DocTypeVersion tuple doesn't imply one should be able to read upper
		versions of this DocTypeExtension.</dd>
		</dl>
		</section>

		<section anchor="doctypeextensionname-element"><name>DocTypeExtensionName Elemen
		t</name>

		<dl>
		<dt>name:</dt>
		<dd>DocTypeExtensionName</dd>
		<dt>path:</dt>
		<dd><tt>\EBML\DocTypeExtension\DocTypeExtensionName</tt></dd>
		<dt>id:</dt>
		<dd>0x4283</dd>
		<dt>minOccurs:</dt>
		<dd>1</dd>
		<dt>maxOccurs:</dt>
		<dd>1</dd>
		<dt>length:</dt>
		<dd>>0</dd>
		<dt>type:</dt>
		<dd>String</dd>
		<dt>description:</dt>
		<dd>The name of the DocTypeExtension to differentiate it from other
		DocTypeExtensions of the same DocType+DocTypeVersion tuple. A DocTypeExtensionNa
		me value
		<bcp14>MUST</bcp14> be unique within the EBML Header.</dd>
		</dl>
		</section>

		<section anchor="doctypeextensionversion-element"><name>DocTypeExtensionVersion
		Element</name>

		<dl>
		<dt>name:</dt>
		<dd>DocTypeExtensionVersion</dd>
		<dt>path:</dt>
		<dd><tt>\EBML\DocTypeExtension\DocTypeExtensionVersion</tt></dd>
		<dt>id:</dt>
		<dd>0x4284</dd>
		<dt>minOccurs:</dt>
		<dd>1</dd>
		<dt>maxOccurs:</dt>
		<dd>1</dd>
		<dt>range:</dt>
		<dd>not 0</dd>
		<dt>type:</dt>
		<dd>Unsigned Integer</dd>
		<dt>description:</dt>
		<dd>The version of the DocTypeExtension. Different DocTypeExtensionVersion
		values of the same DocType + DocTypeVersion + DocTypeExtensionName tuple
		<bcp14>MAY</bcp14> contain completely different sets of extra Elements. An
		EBML Reader <bcp14>MAY</bcp14> support multiple versions
		of the same tuple, only one version of the tuple, or not support the tuple at al
		l.</dd>
		</dl>
		</section>
		</section>

		<section anchor="global-elements"><name>Global Elements</name>
		<t>EBML allows some special Elements to be found within more than one parent
		in an EBML Document or optionally at the Root Level of an EBML Body. These
		Elements are called Global Elements. There are two Global Elements that can be
		found in any EBML Document: the CRC-32 Element and the Void Element. An EBML
		Schema <bcp14>MAY</bcp14> add other Global Elements to the format it
		defines. These extra elements apply only to the EBML Body, not the EBML
		Header.</t>
		<t>Global Elements are EBML Elements whose EBMLLastParent part of the path has
		a GlobalPlaceholder. Because it is the last Parent part of the path, a Global
		Element might also have EBMLParentPath parts in its path. In this case, the
		Global Element can only be found within this EBMLParentPath path -- i.e., it's
		not fully "global".</t>
		<t>A Global Element can be found in many Parent Elements, allowing the same numb
		er of occurrences in each Parent where this Element is found.</t>

		<section anchor="crc-32-element"><name>CRC-32 Element</name>

		<dl>
		<dt>name:</dt>
		<dd>CRC-32</dd>
		<dt>path:</dt>
		<dd><tt>\(1-\)CRC-32</tt></dd>
		<dt>id:</dt>
		<dd>0xBF</dd>
		<dt>minOccurs:</dt>
		<dd>0</dd>
		<dt>maxOccurs:</dt>
		<dd>1</dd>
		<dt>length:</dt>
		<dd>4</dd>
		<dt>type:</dt>
		<dd>Binary</dd>
		<dt>description:</dt>
		<dd>The CRC-32 Element contains a 32-bit Cyclic Redundancy Check value of all
		the Element Data of the Parent Element as stored except for the CRC-32 Element
		itself. When the CRC-32 Element is present, the CRC-32 Element
		<bcp14>MUST</bcp14> be the first ordered EBML Element within its Parent
		Element for easier reading. All Top-Level Elements of an EBML Document that
		are Master Elements <bcp14>SHOULD</bcp14> include a CRC-32 Element as a Child
		Element. The CRC in use is the IEEE-CRC-32 algorithm as used in the
		<xref target="ISO3309"></xref> standard and in Section 8.1.1.6.2 of
		<xref target="ITU.V42"></xref>, with initial value of 0xFFFFFFFF. The CRC value
		<bcp14>MUST</bcp14> be computed on a little-endian bytestream and
		<bcp14>MUST</bcp14> use little-endian storage.</dd>
		</dl>
		</section>

		<section anchor="void-element"><name>Void Element</name>

		<dl>
		<dt>name:</dt>
		<dd>Void</dd>
		<dt>path:</dt>
		<dd><tt>\(-\)Void</tt></dd>
		<dt>id:</dt>
		<dd>0xEC</dd>
		<dt>minOccurs:</dt>
		<dd>0</dd>
		<dt>type:</dt>
		<dd>Binary</dd>
		<dt>description:</dt>
		<dd>Used to void data or to avoid unexpected behaviors when using damaged
		data. The content is discarded. Also used to reserve space in a subelement for
		later use.</dd>
		</dl>
		</section>
		</section>
		</section>

		<section anchor="considerations-for-reading-ebml-data"><name>Considerations for
		Reading EBML Data</name>
		<t>The following scenarios describe events to consider when reading EBML
		Documents, as well as the recommended design of an EBML Reader.</t>
		<t>If a Master Element contains a CRC-32 Element that doesn't validate, then
		the EBML Reader <bcp14>MAY</bcp14> ignore all contained data except for
		Descendant Elements that contain their own valid CRC-32 Element.</t>
		<t>In the following XML representation of a simple, hypothetical EBML
		fragment, a Master Element called CONTACT contains two Child Elements, NAME
		and ADDRESS. In this example, some data within the NAME Element had been
		altered so that the CRC-32 of the NAME Element does not validate, and thus any
		Ancestor Element with a CRC-32 would therefore also no longer
		validate. However, even though the CONTACT Element has a CRC-32 that does not
		validate (because of the changed data within the NAME Element), the CRC-32 of
		the ADDRESS Element does validate, and thus the contents and semantics of the
		ADDRESS Element <bcp14>MAY</bcp14> be used.</t>

		<sourcecode type="xml"><CONTACT>
		<CRC-32>c119a69b</CRC-32><!-- does not validate -->
		<NAME>
		<CRC-32>1f59ee2b</CRC-32><!-- does not validate -->
		<FIRST-NAME>invalid data</FIRST-NAME>
		<LAST-NAME>invalid data</LAST-NAME>
		</NAME>
		<ADDRESS>
		<CRC-32>df941cc9</CRC-32><!-- validates -->
		<STREET>valid data</STREET>
		<CITY>valid data</CITY>
		</ADDRESS>
		</CONTACT>
		</sourcecode>
		<t>If a Master Element contains more occurrences of a Child Master Element
		than permitted according to the <tt>maxOccurs</tt> and <tt>recurring</tt>
		attributes of the
		definition of that Element, then the occurrences in addition to <tt>maxOccurs</t
		t>
		<bcp14>MAY</bcp14> be ignored.</t>
		<t>If a Master Element contains more occurrences of a Child Element than
		permitted according to the <tt>maxOccurs</tt> attribute of the definition of tha
		t
		Element, then all instances of that Element after the first <tt>maxOccurs</tt>
		occurrences from the beginning of its Parent Element <bcp14>SHOULD</bcp14> be
		ignored.</t>
		</section>

		<section anchor="terminating-elements"><name>Terminating Elements</name>
		<t>Null Octets, which are octets with all bits set to zero, <bcp14>MAY</bcp14> f
		ollow the value of a String Element or UTF-8 Element to serve as a terminator.
		An EBML Writer <bcp14>MAY</bcp14> terminate a String Element or UTF-8 Element
		with Null Octets in order to overwrite a stored value with a new value of
		lesser length while maintaining the same Element Data Size; this can prevent
		the need to rewrite large portions of an EBML Document. Otherwise, the use of
		Null Octets within a String Element or UTF-8 Element is <bcp14>NOT RECOMMENDED</
		bcp14>.
		The Element Data of a UTF-8 Element <bcp14>MUST</bcp14>
		be a valid UTF-8 string up to whichever comes first: the end of the Element or
		the first occurring Null octet. Within the Element Data of a String or UTF-8 Ele
		ment,
		any Null octet itself and any following data within that Element
		<bcp14>SHOULD</bcp14> be ignored. A string value and a copy of that string
		value terminated by one or more Null Octets are semantically equal.</t>
		<t><xref target="tableNullOctetSemantics"></xref> shows examples of semantics
		and validation for the use of Null Octets. Values to represent Stored Values
		and the Semantic Meaning as represented as hexadecimal values.</t>
		<table anchor="tableNullOctetSemantics"><name>Examples of semantics for Null
		Octets in VINT_DATA</name>
		<thead>
		<tr>
		<th align="left">Stored Value</th>
		<th align="left">Semantic Meaning</th>
		</tr>
		</thead>

		<tbody>
		<tr>
		<td align="left">0x65 0x62 0x6D 0x6C</td>
		<td align="left">0x65 0x62 0x6D 0x6C</td>
		</tr>

		<tr>
		<td align="left">0x65 0x62 0x00 0x6C</td>
		<td align="left">0x65 0x62</td>
		</tr>

		<tr>
		<td align="left">0x65 0x62 0x00 0x00</td>
		<td align="left">0x65 0x62</td>
		</tr>

		<tr>
		<td align="left">0x65 0x62</td>
		<td align="left">0x65 0x62</td>
		</tr>
		</tbody>
		</table></section>

		<section anchor="guidelines-for-updating-elements"><name>Guidelines for Updating
		Elements</name>
		<t>An EBML Document can be updated without requiring that the entire EBML
		Document be rewritten. These recommendations describe strategies for changing
		the Element Data of a written EBML Element with minimal disruption to the rest
		of the EBML Document.</t>

		<section anchor="reducing-element-data-in-size"><name>Reducing Element Data in S
		ize</name>
		<t>There are three methods to reduce the size of Element Data of a written EBML
		Element.</t>

		<section anchor="adding-a-void-element"><name>Adding a Void Element</name>
		<t>When an EBML Element is changed to reduce its total length by more than one o
		ctet, an EBML Writer <bcp14>SHOULD</bcp14> fill the freed space with a Void Elem
		ent.</t>
		</section>

		<section anchor="extending-the-element-data-size"><name>Extending the Element Da
		ta Size</name>
		<t>The same value for Element Data Size <bcp14>MAY</bcp14> be written in various
		lengths, so for minor reductions of the Element Data, the Element Size <bcp14>M
		AY</bcp14> be written to a longer octet length to fill the freed space.</t>
		<t>For example, the first row of
		<xref target="tableShortenVintOneOctet"></xref> depicts a String Element that st
		ores
		an Element ID (3 octets), Element Data Size (1 octet), and Element Data (4
		octets). If the Element Data is changed to reduce the length by one octet, and
		if the current length of the Element Data Size is less than its maximum
		permitted length, then the Element Data Size of that Element
		<bcp14>MAY</bcp14> be rewritten to increase its length by one octet. Thus,
		before and after the change, the EBML Element maintains the same length of 8
		octets, and data around the Element does not need to be moved.</t>
		<table anchor="tableShortenVintOneOctet"><name>Example of editing a VINT to
		reduce VINT_DATA length by one octet</name>
		<thead>
		<tr>
		<th>Status</th>
		<th>Element ID</th>
		<th>Element Data Size</th>
		<th>Element Data</th>
		</tr>
		</thead>

		<tbody>
		<tr>
		<td>Before edit</td>
		<td>0x3B4040</td>
		<td>0x84</td>
		<td>0x65626D6C</td>
		</tr>

		<tr>
		<td>After edit</td>
		<td>0x3B4040</td>
		<td>0x4003</td>
		<td>0x6D6B76</td>
		</tr>
		</tbody>
		</table><t>This method is <bcp14>RECOMMENDED</bcp14> when the Element Data is
		reduced by a single octet; for reductions by two or more octets, it is
		<bcp14>RECOMMENDED</bcp14> to fill the freed space with a Void Element.</t>
		<t>Note that if the Element Data length needs to be rewritten as shortened by
		one octet and the Element Data Size could be rewritten as a shorter VINT, then
		it is <bcp14>RECOMMENDED</bcp14> to rewrite the Element Data Size as one octet
		shorter, shorten the Element Data by one octet, and follow that Element with a
		Void Element. For example,
		<xref target="tableShortenVintMoreThanOneOctet"></xref> depicts a String Element
		that stores an Element ID (3 octets), Element Data Size (2 octets, but could
		be rewritten in one octet), and Element Data (3 octets). If the Element Data
		is to be rewritten to a two-octet length, then another octet can be taken from
		Element Data Size so that there is enough space to add a two-octet Void
		Element.</t>
		<table anchor="tableShortenVintMoreThanOneOctet"><name>Example of editing a
		VINT to reduce VINT_DATA length by more than one octet</name>
		<thead>
		<tr>
		<th>Status</th>
		<th>Element ID</th>
		<th>Element Data Size</th>
		<th>Element Data</th>
		<th>Void Element</th>
		</tr>
		</thead>

		<tbody>
		<tr>
		<td>Before</td>
		<td>0x3B4040</td>
		<td>0x4003</td>
		<td>0x6D6B76</td>
		<td></td>
		</tr>

		<tr>
		<td>After</td>
		<td>0x3B4040</td>
		<td>0x82</td>
		<td>0x6869</td>
		<td>0xEC80</td>
		</tr>
		</tbody>
		</table></section>

		<section anchor="terminating-element-data"><name>Terminating Element Data</name>
		<t>For String Elements and UTF-8 Elements, the length of Element Data could be
		reduced by adding Null Octets to terminate the Element Data (see
		<xref target="terminating-elements"></xref>).</t>
		<t>In <xref target="tableExampleNullPadding"></xref>, Element Data four octets
		long is changed to a value three octets long, followed by a Null Octet; the
		Element Data Size includes any Null Octets used to terminate Element Data and th
		erefore
		remains unchanged.</t>
		<table anchor="tableExampleNullPadding"><name>Example of terminating VINT_DATA
		with a Null Octet when reducing VINT length during an edit</name>
		<thead>
		<tr>
		<th>Status</th>
		<th>Element ID</th>
		<th>Element Data Size</th>
		<th>Element Data</th>
		</tr>
		</thead>

		<tbody>
		<tr>
		<td>Before edit</td>
		<td>0x3B4040</td>
		<td>0x84</td>
		<td>0x65626D6C</td>
		</tr>

		<tr>
		<td>After edit</td>
		<td>0x3B4040</td>
		<td>0x84</td>
		<td>0x6D6B7600</td>
		</tr>
		</tbody>
		</table><t>Note that this method is <bcp14>NOT RECOMMENDED</bcp14>. For
		reductions of one octet, the method for Extending the Element Data Size
		<bcp14>SHOULD</bcp14> be used. For reduction by more than one octet, the
		method for Adding a Void Element <bcp14>SHOULD</bcp14> be used.</t>
		</section>
		</section>

		<section anchor="considerations-when-updating-elements-with-cyclic-redundancy-ch
		eck-crc"><name>Considerations when Updating Elements with Cyclic Redundancy Chec
		k (CRC)</name>
		<t>If the Element to be changed is a Descendant Element of any Master Element
		that contains a CRC-32 Element (see <xref target="crc-32-element"></xref>),
		then the CRC-32 Element <bcp14>MUST</bcp14> be verified before permitting the
		change. Additionally, the CRC-32 Element value <bcp14>MUST</bcp14> be
		subsequently updated to reflect the changed data.</t>
		</section>
		</section>

		<section anchor="backward-and-forward-compatibility"><name>Backward and Forward
		Compatibility</name>
		<t>Elements of an EBML format <bcp14>SHOULD</bcp14> be designed with backward an
		d forward compatibility in mind.</t>

		<section anchor="backward-compatibility"><name>Backward Compatibility</name>
		<t>Backward compatibility of new EBML Elements can be achieved by using default
		values for mandatory elements. The default value <bcp14>MUST</bcp14> represent t
		he state that was assumed for previous versions of the EBML Schema, without this
		new EBML Element. If such a state doesn't make sense for previous versions, the
		n the new EBML Element <bcp14>SHOULD NOT</bcp14> be mandatory.</t>
		<t>Non-mandatory EBML Elements can be added in a new EBMLDocTypeVersion. Since
		they are not mandatory, they won't be found in older versions of the
		EBMLDocTypeVersion, just as they might not be found in newer versions. This
		causes no compatibility issue.</t>
		</section>

		<section anchor="forward-compatibility"><name>Forward Compatibility</name>
		<t>EBML Elements <bcp14>MAY</bcp14> be marked as deprecated in a new
		EBMLDocTypeVersion using the <tt>maxver</tt> attribute of the EBML Schema. If su
		ch an
		Element is found in an EBML Document with a newer version of the
		EBMLDocTypeVersion, it <bcp14>SHOULD</bcp14> be discarded.</t>
		</section>
		</section>

		<section anchor="security-considerations"><name>Security Considerations</name>
		<t>EBML itself does not offer any kind of security and does not provide confiden
		tiality. EBML does not provide any kind of authorization. EBML only offers margi
		nally useful and effective data integrity options, such as CRC elements.</t>
		<t>Even if the semantic layer offers any kind of encryption, EBML itself could
		leak information at both the semantic layer (as declared via the DocType
		Element) and within the EBML structure (the presence of EBML Elements can be
		derived even with an unknown semantic layer using a heuristic approach -- not
		without errors, of course, but with a certain degree of confidence).</t>
		<t>An EBML Document that has the following issues may still be handled by the
		EBML Reader and the data accepted as such, depending on how strict the EBML
		Reader wants to be:</t>

		<ul>
		<li><t>Invalid Element IDs that are longer than the limit stated in the EBMLMaxI
		DLength Element of the EBML Header.</t>
		</li>
		<li><t>Invalid Element IDs that are not encoded in the shortest-possible way.</t
		>
		</li>
		<li><t>Invalid Element Data Size values that are longer than the limit stated in
		the EBMLMaxSizeLength Element of the EBML Header.</t>
		</li>
		</ul>
		<t>Element IDs that are unknown to the EBML Reader <bcp14>MAY</bcp14> be
		accepted as valid EBML IDs in order to skip such elements.</t>
		<t>EBML Elements with a string type may contain extra data after the first
		0x00. These data <bcp14>MUST</bcp14> be discarded according to the
		<xref target="terminating-elements"></xref> rules.</t>
		<t>An EBML Reader may discard some or all data if the following errors are found
		in the EBML Document:</t>

		<ul>
		<li><t>Invalid Element Data Size values (e.g., extending the length of the EBML
		Element beyond the scope of the Parent Element, possibly triggering access-out-o
		f-bounds issues).</t>
		</li>
		<li><t>Very high lengths in order to force out-of-memory situations resulting in
		a denial of service, access-out-of-bounds issues, etc.</t>
		</li>
		<li><t>Missing EBML Elements that are mandatory in a Master Element and have no
		declared default value, making the semantic invalid at that Master Element level
		.</t>
		</li>
		<li><t>Usage of invalid UTF-8 encoding in EBML Elements of UTF-8 type (e.g., in
		order to trigger access-out-of-bounds or buffer-overflow issues).</t>
		</li>
		<li><t>Usage of invalid data in EBML Elements with a date type, triggering bogus
		date accesses.</t>
		</li>
		<li><t>The CRC-32 Element (see <xref target="crc-32-element"></xref>) of a Maste
		r Element doesn't match the rest of the content of that Master Element.</t>
		</li>
		</ul>
		<t>Side-channel attacks could exploit:</t>

		<ul>
		<li><t>The semantic equivalence of the same string stored in a String Element or
		UTF-8 Element with and without zero-bit padding, making comparison at the seman
		tic level invalid.</t>
		</li>
		<li><t>The semantic equivalence of VINT_DATA within Element Data Size with two d
		ifferent lengths due to left-padding zero bits, making comparison at the semanti
		c level invalid.</t>
		</li>
		<li><t>Data contained within a Master Element that is not itself part of a Child
		Element, which can trigger incorrect parsing behavior in EBML Readers.</t>
		</li>
		<li><t>Extraneous copies of Identically Recurring Element, making parsing unnece
		ssarily slow to the point of not being usable.</t>
		</li>
		<li><t>Copies of Identically Recurring Element within a Parent Element that cont
		ain invalid CRC-32 Elements. EBML Readers not checking the CRC-32 might use the
		version of the element with mismatching CRC-32s.</t>
		</li>
		<li><t>Use of Void Elements that could be used to hide content or create bogus r
		esynchronization points seen by some EBML Readers and not others.</t>
		</li>
		</ul>
		</section>

		<section anchor="iana-considerations"><name>IANA Considerations</name>

		<section anchor="ebml-element-ids-registry"><name>EBML Element IDs Registry</nam
		e>
		<t>This document creates a new IANA registry called the
		"EBML Element IDs" registry.</t>
		<t>Element IDs are described in <xref target="element-id"></xref>. Element
		IDs are encoded using the VINT mechanism described in
		<xref target="variable-size-integer"></xref> and can be between one and five
		octets long. Five-octet-long Element IDs are possible only if declared
		in the header.</t>
		<t>This IANA registry only applies to Elements that can be contained
		in the EBML Header, thus including Global Elements. Elements only
		found in the EBML Body have their own set of independent Element IDs
		and are not part of this IANA registry.</t>
		<t>One-octet Element IDs <bcp14>MUST</bcp14> be between 0x81 and
		0xFE. These items are valuable because they are short, and they need
		to be used for commonly repeated elements. Element IDs are to be
		allocated within this range according to the "RFC Required"
		policy <xref target="RFC8126"></xref>.</t>
		<t>The following one-octet Element IDs are RESERVED: 0xFF and
		0x80.</t>
		<t>Values in the one-octet range of 0x00 to 0x7F are not valid for use
		as an Element ID.</t>
		<t>Two-octet Element IDs <bcp14>MUST</bcp14> be between 0x407F and
		0x7FFE. Element IDs are to be allocated within this range according to
		the "Specification Required" policy
		<xref target="RFC8126"></xref>.</t>
		<t>The following two-octet Element IDs are RESERVED: 0x7FFF and
		0x4000.</t>
		<t>Values in the two-octet ranges of 0x0000 to 0x3FFF and 0x8000 to 0xFFFF are
		not valid for use as an Element ID.</t>
		<t>Three-octet Element IDs <bcp14>MUST</bcp14> be between 0x203FFF and 0x3FFFFE.
		Element IDs are to be allocated within this range according to the "First
		Come First Served" policy <xref target="RFC8126"></xref>.</t>
		<t>The following three-octet Element IDs are RESERVED: 0x3FFFFF and
		0x200000.</t>
		<t>Values in the three-octet ranges of 0x000000 to 0x1FFFFF and
		0x400000 to 0xFFFFFF are not valid for use as an Element ID.</t>
		<t>Four-octet Element IDs <bcp14>MUST</bcp14> be between 0x101FFFFF
		and 0x1FFFFFFE. Four-octet Element IDs are somewhat special in that
		they are useful for resynchronizing to major structures in the event
		of data corruption or loss. As such, four-octet Element IDs are split
		into two categories. Four-octet Element IDs whose lower three octets
		(as encoded) would make printable 7-bit ASCII values (0x20 to 0x7E,
		inclusive) <bcp14>MUST</bcp14> be allocated by the "Specification
		Required" policy. Sequential allocation of values is not
		required: specifications <bcp14>SHOULD</bcp14> include a specific
		request and are encouraged to do early allocations.</t>
		<t>To be clear about the above category: four-octet Element IDs always start
		with hex 0x10 to 0x1F, and that octet may be chosen so that the entire VINT
		has some desirable property, such as a specific CRC. The other three octets,
		when ALL having values between 0x20 (32, ASCII Space) and 0x7E (126, ASCII
		"~"), fall into this category.</t>
		<t>Other four-octet Element IDs may be allocated by the "First Come First S
		erved" policy.</t>
		<t>The following four-octet Element IDs are RESERVED: 0x1FFFFFFF and 0x10000000
		.</t>
		<t>Values in the four-octet ranges of 0x00000000 to 0x0FFFFFFF and 0x20000000
		to 0xFFFFFFFF are not valid for use as an Element ID.</t>
		<t>Five-octet Element IDs (values from 0x080FFFFFFF to 0x0FFFFFFFFE) are RESERVE
		D according to the "Experimental Use" policy <xref target="RFC8126"></
		xref>: they may be used by anyone at any time, but there is no coordination.</t>
		<t>ID Values found in this document are assigned as initial values as follows:</
		t>
		<table><name>IDs and Names for EBML Elements assigned by this document
		</name>
		<thead>
		<tr>
		<th align="right">Element ID</th>
		<th align="left">Element Name</th>
		<th align="left">Reference</th>
		</tr>
		</thead>

		<tbody>
		<tr>
		<td align="right">0x1A45DFA3</td>
		<td align="left">EBML</td>
		<td align="left">Described in <xref target="ebml-element"></xref></td>
		</tr>

		<tr>
		<td align="right">0x4286</td>
		<td align="left">EBMLVersion</td>
		<td align="left">Described in <xref target="ebmlversion-element"></xref></td>
		</tr>

		<tr>
		<td align="right">0x42F7</td>
		<td align="left">EBMLReadVersion</td>
		<td align="left">Described in <xref target="ebmlreadversion-element"></xref></td
		>
		</tr>

		<tr>
		<td align="right">0x42F2</td>
		<td align="left">EBMLMaxIDLength</td>
		<td align="left">Described in <xref target="ebmlmaxidlength-element"></xref></td
		>
		</tr>

		<tr>
		<td align="right">0x42F3</td>
		<td align="left">EBMLMaxSizeLength</td>
		<td align="left">Described in <xref target="ebmlmaxsizelength-element"></xref></
		td>
		</tr>

		<tr>
		<td align="right">0x4282</td>
		<td align="left">DocType</td>
		<td align="left">Described in <xref target="doctype-element"></xref></td>
		</tr>

		<tr>
		<td align="right">0x4287</td>
		<td align="left">DocTypeVersion</td>
		<td align="left">Described in <xref target="doctypeversion-element"></xref></td>
		</tr>

		<tr>
		<td align="right">0x4285</td>
		<td align="left">DocTypeReadVersion</td>
		<td align="left">Described in <xref target="doctypereadversion-element"></xref><
		/td>
		</tr>

		<tr>
		<td align="right">0x4281</td>
		<td align="left">DocTypeExtension</td>
		<td align="left">Described in <xref target="doctypeextension-element"></xref></t
		d>
		</tr>

		<tr>
		<td align="right">0x4283</td>
		<td align="left">DocTypeExtensionName</td>
		<td align="left">Described in <xref target="doctypeextensionname-element"></xref
		></td>
		</tr>

		<tr>
		<td align="right">0x4284</td>
		<td align="left">DocTypeExtensionVersion</td>
		<td align="left">Described in <xref target="doctypeextensionversion-element"></x
		ref></td>
		</tr>

		<tr>
		<td align="right">0xBF</td>
		<td align="left">CRC-32</td>
		<td align="left">Described in <xref target="crc-32-element"></xref></td>
		</tr>

		<tr>
		<td align="right">0xEC</td>
		<td align="left">Void</td>
		<td align="left">Described in <xref target="void-element"></xref></td>
		</tr>
		</tbody>
		</table></section>

		<section anchor="ebml-doctypes-registry"><name>EBML DocTypes Registry</name>
		<t>This document creates a new IANA registry called the "EBML DocTypes&quot
		; registry.</t>
		<t>To register a new DocType in this registry, one needs a DocType name, a Descr
		iption of the DocType, a Change Controller (IESG or email of registrant), and an
		optional Reference to a document describing the DocType.</t>
		<t>DocType values are described in <xref target="doctype"></xref>. DocTypes
		are ASCII strings, defined in <xref target="string-element"></xref>, which
		label the official name of the EBML Document Type. The strings may be
		allocated according to the "First Come First Served" policy.</t>
		<t>The use of ASCII corresponds to the types and code already in use; the
		value is not meant to be visible to the user.</t>
		<t>DocType string values of "matroska" and "webm" are RESERV
		ED to the IETF for future use.
		These can be assigned via the "IESG Approval" or "RFC Required&qu
		ot; policies <xref target="RFC8126"></xref>.</t>
		</section>
		</section>

		</middle>

		<back>
		<displayreference target="I-D.ietf-cellar-matroska" to="Matroska"/>
		<references><name>Normative References</name>
		<reference anchor="IEEE.754" target="https://standards.ieee.org/standard/754-201
		9.html">
		<front>
		<title>IEEE Standard for Binary Floating-Point Arithmetic</title>
		<author>
		<organization>IEEE</organization>
		</author>
		<date year="2019" month="June" day="13"></date>
		</front>
		</reference>
		<reference anchor="ISO3309" target="https://www.iso.org/standard/8558.html">
		<front>
		<title>Data communication -- High-level data link control procedures -- Fram
		e structure</title>
		<author>
		<organization>International Organization for Standardization</organization
		>
		</author>
		<date year="1984" month="October"></date>
		</front>
		<seriesInfo name="ISO" value="3309, 3rd Edition"></seriesInfo>
		</reference>
		<reference anchor="ISO9899" target="https://www.iso.org/standard/57853.html">
		<front>
		<title>Information technology -- Programming languages -- C</title>
		<author>
		<organization>International Organization for Standardization</organization
		>
		</author>
		<date year="2011"></date>
		</front>
		<seriesInfo name="ISO/IEC" value="9899:2011"></seriesInfo>
		</reference>
		<reference anchor="ITU.V42" target="https://www.itu.int/rec/T-REC-V.42">
		<front>
		<title>Error-correcting procedures for DCEs using asynchronous-to-synchronou
		s conversion</title>
		<author>
		<organization>International Telecommunications Union</organization>
		</author>
		<date year="2002" month="March"></date>
		</front>
		<seriesInfo name="ITU-T Recommendation" value="V.42"></seriesInfo>
		</reference>
		<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.0020.
		xml"/>
		<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2119.
		xml"/>
		<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2141.
		xml"/>
		<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.2648.
		xml"/>
		<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3339.
		xml"/>
		<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3629.
		xml"/>
		<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.3688.
		xml"/>
		<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5234.
		xml"/>
		<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.5646.
		xml"/>
		<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.7405.
		xml"/>
		<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8126.
		xml"/>
		<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml/reference.RFC.8174.
		xml"/>
		<reference anchor="XHTML" target="https://www.w3.org/TR/2018/SPSD-xhtml-basic-20
		180327/">
		<front>
		<title>XHTML(tm) Basic 1.1 -- Second Edition</title>
		<author fullname="Shane McCarron" initials="S." surname="McCarron">

		</author>
		<date year="2018" month="March" day="27"></date>
		</front>
		<seriesInfo name="Latest version available at" value="https://www.w3.org/TR/xh
		tml-basic"></seriesInfo>
		</reference>
		<reference anchor="XML" target="https://www.w3.org/TR/2008/REC-xml-20081126/">
		<front>
		<title>Extensible Markup Language (XML) 1.0 (Fifth Edition)</title>
		<author initials="T." surname="Bray" role="editor">
		<organization>Textuality and Netscape</organization>
		</author>
		<author initials="J" surname="Paoli" role="editor">

		</author>
		<author initials="C.M" surname="Sperberg-McQueen" role="editor">

		</author>
		<author initials="E." surname="Maler" role="editor">

		</author>
		<author initials="F." surname="Yergeau" role="editor">

		</author>
		<date year="2008" month="November" day="26"></date>
		</front>
		<seriesInfo name="Latest version available at" value="https://www.w3.org/TR/xm
		l/"></seriesInfo>
		</reference>
		<reference anchor="XML-SCHEMA" target="https://www.w3.org/TR/2004/REC-xmlschema-
		0-20041028/">
		<front>
		<title>XML Schema Part 0: Primer Second Edition</title>
		<author fullname="David C. Fallside" initials="D.C." surname="Fallside">

		</author>
		<author fullname="Priscilla Walmsley" initials="P" surname="Walmsley">

		</author>
		<date year="2004" month="October" day="28"></date>
		</front>
		<seriesInfo name="Latest version available at" value="http://www.w3.org/TR/xml
		schema-0/"></seriesInfo>
		</reference>
		</references>
		<references><name>Informative References</name>

		<xi:include href="https://xml2rfc.ietf.org/public/rfc/bibxml-ids/reference.I-D.i
		etf-cellar-matroska.xml"/>

		<reference anchor="WebM" target="https://www.webmproject.org/docs/container/">
		<front>
		<title>WebM Container Guidelines</title>
		<author>
		<organization>The WebM Project</organization>
		</author>
		<date year="2017" month="November" day="28"></date>
		</front>
		</reference>

		<reference anchor="XPath" target="https://www.w3.org/TR/1999/REC-xpath-19991116"
		>
		<front>
		<title>XML Path Language (XPath) Version 1.0</title>
		<author initials="J." surname="Clark" role="editor">

		</author>
		<author initials="S" surname="DeRose">

		</author>
		<date year="1999" month="November" day="16"></date>
		</front>
		<seriesInfo name="Latest version available at" value="https://www.w3.org/TR/xp
		ath"></seriesInfo>
		</reference>

		</references>

		</back>

		</rfc>

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