cellar                                                         S. Lhomme
Internet-Draft
Intended status: Standards Track                                 D. Rice
Expires: March 27, April 14, 2017
                                                               M. Bunkus
                                                      September 23,
                                                        October 11, 2016

                    Extensible Binary Meta Language
                       draft-ietf-cellar-ebml-00
                       draft-ietf-cellar-ebml-01

Abstract

   This document defines the Extensible Binary Meta Language (EBML)
   format as a genearlized generalized file format for any type of data in a
   hierarchical form.  EBML is designed as a binary equivalent to XML
   and utilizes uses a storage-efficient approach to building build nested Elements with
   identifiers, lengths, and values.  Similar to how an XML Schema
   defines the structure and semantics of an XML Document, this document
   defines an how EBML Schema Schemas are created to convey the semantics of an
   EBML Document.

Status of This Memo

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   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on March 27, April 14, 2017.

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   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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   described in the Simplified BSD License.

Table of Contents

   1.  EBML specifications . . . . .  Introduction  . . . . . . . . . . . . . . . .   2
     1.1.  Introduction . . . . . . . .   3
   2.  Notation and Conventions  . . . . . . . . . . . . . .   2
     1.2.  Notation and Conventions . . . .   3
   3.  Security Considerations . . . . . . . . . . . .   3
     1.3.  Security Considerations . . . . . . .   5
   4.  Structure . . . . . . . . . .   3
     1.4.  Structure . . . . . . . . . . . . . . . .   7
   5.  Variable Size Integer . . . . . . . .   4
     1.5.  Variable Size Integer . . . . . . . . . . . .   7
     5.1.  VINT_WIDTH  . . . . . .   4
       1.5.1.  VINT_WIDTH . . . . . . . . . . . . . . . . .   7
     5.2.  VINT_MARKER . . . .   4
       1.5.2.  VINT_MARKER . . . . . . . . . . . . . . . . . . .   7
     5.3.  VINT_DATA . .   4
       1.5.3.  VINT_DATA . . . . . . . . . . . . . . . . . . . . . .   4
       1.5.4.   8
     5.4.  VINT Examples . . . . . . . . . . . . . . . . . . . .   5
     1.6. . .   8
   6.  Element ID  . . . . . . . . . . . . . . . . . . . . . . .   5
     1.7. . .   9
   7.  Element Data Size . . . . . . . . . . . . . . . . . . . .   6
     1.8. . .  10
   8.  EBML Element Types  . . . . . . . . . . . . . . . . . . .   8
     1.9.  EBML Document . .  12
     8.1.  Signed Integer Element  . . . . . . . . . . . . . . . . .  13
     8.2.  Unsigned Integer Element  . . .  11
       1.9.1.  EBML Header . . . . . . . . . . . . .  13
     8.3.  Float Element . . . . . . . .  12
       1.9.2.  EBML Body . . . . . . . . . . . . . .  13
     8.4.  String Element  . . . . . . . . .  12
     1.10. EBML Stream . . . . . . . . . . . .  13
     8.5.  UTF-8 Element . . . . . . . . . . .  13
     1.11. Elements semantic . . . . . . . . . . .  14
     8.6.  Date Element  . . . . . . . . .  13
       1.11.1. . . . . . . . . . . . . .  14
     8.7.  Master Element  . . . . . . . . . . . . . . . . . . . . .  14
     8.8.  Binary Element  . . . . . . . . . . . . . . . . . . . . .  15
   9.  EBML Schema Document . . . . . . . . . . . . . . . . . . . .  13
       1.11.2. . . . .  15
     9.1.  EBML Header Elements . . . . . . . . . . . . . . . .  22
       1.11.3.  Global elements (used everywhere in the format) . .  25
     2.1.  URIs . . . . .  15
     9.2.  EBML Body . . . . . . . . . . . . . . . . . . . . .  27
   Authors' Addresses . . .  16
   10. EBML Stream . . . . . . . . . . . . . . . . . . . .  27

1.  EBML specifications

1.1.  Introduction

   EBML, short for Extensible Binary Meta Language, specifies a binary
   and octet (byte) aligned format inspired by the principle of XML.

   The goal of the . . . . .  16
   11. Elements semantic . . . . . . . . . . . . . . . . . . . . . .  16
     11.1.  EBML Specification is to define a generic, binary,
   space-efficient format that may Schema  . . . . . . . . . . . . . . . . . . . . . .  16
       11.1.1.  Element  . . . . . . . . . . . . . . . . . . . . . .  17
       11.1.2.  Attributes . . . . . . . . . . . . . . . . . . . . .  17
       11.1.3.  Element  . . . . . . . . . . . . . . . . . . . . . .  18
       11.1.4.  Attributes . . . . . . . . . . . . . . . . . . . . .  18
       11.1.5.  Element  . . . . . . . . . . . . . . . . . . . . . .  23
       11.1.6.  Attributes . . . . . . . . . . . . . . . . . . . . .  23
       11.1.7.  EBML Schema Example  . . . . . . . . . . . . . . . .  23
       11.1.8.  Identically Recurring Elements . . . . . . . . . . .  24
       11.1.9.  Expression of range  . . . . . . . . . . . . . . . .  25
       11.1.10. Textual expression of Floats . . . . . . . . . . . .  25
       11.1.11. Note on the Use of default attributes to define
                Mandatory EBML Elements  . . . . . . . . . . . . . .  26
     11.2.  EBML Header Elements . . . . . . . . . . . . . . . . . .  27
       11.2.1.  EBML Element . . . . . . . . . . . . . . . . . . . .  27
       11.2.2.  EBMLVersion Element  . . . . . . . . . . . . . . . .  27
       11.2.3.  EBMLReadVersion Element  . . . . . . . . . . . . . .  28
       11.2.4.  EBMLMaxIDLength Element  . . . . . . . . . . . . . .  28
       11.2.5.  EBMLMaxSizeLength Element  . . . . . . . . . . . . .  29
       11.2.6.  DocType Element  . . . . . . . . . . . . . . . . . .  29
       11.2.7.  DocTypeVersion Element . . . . . . . . . . . . . . .  30
       11.2.8.  DocTypeReadVersion Element . . . . . . . . . . . . .  30
     11.3.  Global elements (used everywhere in the format)  . . . .  30
       11.3.1.  Void Element . . . . . . . . . . . . . . . . . . . .  31
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .  31
     12.1.  Normative References . . . . . . . . . . . . . . . . . .  31
     12.2.  Informative References . . . . . . . . . . . . . . . . .  33
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  33

1.  Introduction

   "EBML", short for Extensible Binary Meta Language, specifies a binary
   and octet (byte) aligned format inspired by the principle of XML (a
   framework for structuring data).

   The goal of this document is to define a generic, binary, space-
   efficient format that can be used to define more complex formats
   (such as containers for multimedia content) using an "EBML Schema".
   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 utilized defined.

   "EBML" uses a simple approach of building "Elements" upon three
   pieces of data (tag, length, and value) as this approach is well
   known, easy to define more parse, and allows selective data parsing.  The "EBML"
   structure additionally allows for hierarchical arrangement to support
   complex structural formats (such in an efficient manner.

2.  Notation and Conventions

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as containers described in [RFC2119].

   This document defines specific terms in order to define the format
   and application of "EBML".  Specific terms are defined below:

   "Child Element": A "Child Element" is a relative term to describe the
   "EBML Elements" immediately contained within a "Master Element".

   "EBML": Extensible Binary Meta Language

   "Element Data": The value(s) of the "EBML Element" which is
   identified by its "Element ID" and "Element Data Size".  The form of
   the "Element Data" is defined by this document and the corresponding
   "EBML Schema" of the Element's "EBML Document Type".

   "Element Data Size": An expression, encoded as a "Variable Size
   Integer", of the length in octets of "Element Data".

   "EBML Body": All data of an "EBML Document" following the "EBML
   Header" may be considered the "EBML Body".

   "EBML Class": An representation of the octet length of an "Element
   ID".

   "EBML Document": An "EBML Document" is a datastream comprised of only
   two components, an "EBML Header" and an "EBML Body".

   "EBML Document Type": An "EBML Document Type" is a name provided by
   an "EBML Schema" for multimedia content) using a particular implementation of "EBML" for a data
   format (examples: matroska and webm).

   "EBML Element": A foundation block of data that contains three parts:
   an EBML
   Schema. "Element ID", an "Element Data Size", and "Element Data".

   "EBML Header": The "EBML Header" is a declaration that provides
   processing instructions and identification of the "EBML Body".  The
   "EBML Header" may be considered as analogous to an XML Declaration.

   "EBML Schema": A standardized definition for the structure of an
   "EBML Document Type".

   "EBML Stream": An "EBML Stream" is a file that consists of one or
   many "EBML Documents" that are concatenated together.

   "Element ID": The "Element ID" is a binary value, encoded as a
   "Variable Size Integer", used to uniquely identify a defined "EBML
   Element" within a specific "EBML Schema".

   "Element Name": The definition official human-readable name of the EBML format recognizes the idea behind
   HTML and XML as a good one: separate structure and semantics allowing "EBML
   Element".

   "Element Path": The hierarchy of "Parent Element" where the same structural layer "EBML
   Element" is expected to be used with multiple, possibly widely
   differing semantic layers.  Except for found in the EBML Header and a few
   global elements this specification does not define particular EBML
   format semantics; however this specification "EBML Body".

   "Empty Element": An "Empty Element" is intended an "EBML Element" that has an
   "Element Data Size" with all VINT_DATA bits set to define
   how other EBML-based formats may be defined.

   EBML uses a simple approach of building Elements upon three pieces zero which
   indicates that the "Element Data" of
   data (tag, length, and value) as this approach the Element is well known, easy to
   parse, and allows selective data parsing. zero octets in
   length.

   "Master Element": The EBML structure
   additionally allows for hierarchical arrangement "Master Element" contains zero, one, or many
   other "EBML Elements".

   "Parent Element": A relative term to support complex
   structural formats in describe the "Master Element"
   which contains a specified element.

   "Root Element": A mandatory, non-repeating "EBML Element" which
   occurs at the top level of the path hierarchy within an efficient manner.

1.2.  Notation "EBML Body"
   and Conventions contains all other "EBML Elements" of the "EBML Body", excepting
   optional "Void Elements".

   "Root Level": The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" starting level in this
   document are to the hierarchy of an "EBML
   Document".

   "Top-Level Element": An "EBML Element" defined as a "Child Element"
   of the "Root Element".

   "Unknown-Sized Element": An Element with an unknown "Element Data
   Size".

   "Variable Size Integer": A compact variable-length binary value which
   defines its own length.

   "VINT": Also known as "Variable Size Integer".

   "VINTMAX": The maximum possible value that can be interpreted stored as described in RFC 2119 [1].

1.3. "Element
   Data Size".

3.  Security Considerations

   EBML

   "EBML" itself does not offer any kind of security.  It has nothing to
   do with authentication, it kind of security and does not
   provide confidentiality, only
   marginally useful and effective data integrity options (CRC
   elements).

   EBML confidentiality.  "EBML" does not provide any kind of
   authorization.  EBML only offers marginally useful and effective data
   integrity options, such as CRC elements.

   Even if the semantic layer offers any kind of encryption, EBML "EBML"
   itself
   may could leak information at both the semantic layer (as declared
   via the DocType element) and within the EBML "EBML" structure (you can
   derive the presence of EBML elements even with an unknown semantic
   layer with a heuristic approach; not without errors, of course, but
   with a certain degree of confidence).

   Attacks on an EBML reader may "EBML Reader" could include: -

   o  Invalid Element IDs "Element IDs" that are longer than the limit stated in the EBMLMaxIDLength Element
      "EBMLMaxIDLength Element" of the
   EBML Header.  - "EBML Header".

   o  Invalid Element IDs "Element IDs" that are not encoded in the
   shortest-possible shortest-
      possible way.  -

   o  Invalid Element IDs "Element IDs" comprised of reserved values.  -

   o  Invalid Element "Element Data Size Size" values that are longer than the limit
      stated in the EBMLMaxSizeLength Element "EBMLMaxSizeLength Element" of the EBML Header.  - "EBML Header".

   o  Invalid Element "Element Data Size Size" values (e.g. extending the length of
      the
   Element "EBML Element" beyond the scope of the Parent Element; "Parent Element";
      possibly triggering access-out-of-bounds issues).  -

   o  Very high lengths in order to force out-of-memory situations
      resulting in a denial of service, access-
   out-of-bounds access-out-of-bounds issues etc.  -

   o  Missing Elements "EBML Elements" that are mandatory and have no declared
      default value.  -

   o  Usage of 0x00 "0x00" octets in EBML
   Elements "EBML Elements" with a string type.  -

   o  Usage of invalid UTF-8 encoding in
   EBML Elements "EBML Elements" of UTF-8 type
      (e.g. in order to trigger access-out-of-
   bounds access-out-of-bounds or buffer overflow
      issues).  -

   o  Usage of invalid data in EBML
   Elements "EBML Elements" with a date type.

1.4.

   Side channel attacks could exploit:

   o  The semantic equivalence of the same string stored in a "String
      Element" or "UTF-8 Element" with and without zero-bit padding.

   o  The semantic equivalence of "VINT_DATA" within "Element Data Size"
      with to different lengths due to left-padding zero bits.

   o  Data contained within a "Master Element" which is not itself part
      of an "EBML Element".

   o  Extraneous copies of "Identically Recurring Element".

   o  Copies of "Identically Recurring Element" within a "Parent
      Element" that contains an invalid "CRC-32 Elements".

   o  Use of "Void Elements".

4.  Structure

   EBML

   "EBML" uses a system of Elements to compose an EBML Document.  Elements "EBML Document".
   "EBML Elements" incorporate three parts: an Element ID, "Element ID", an Element "Element
   Data Size, Size", and
   Element Data. "Element Data".  The Element Data, "Element Data", which is
   described by the Element
   ID, may include "Element ID", includes either binary data or data, one or
   many other Elements.

1.5. "EBML Elements", or both.

5.  Variable Size Integer

   The Element ID "Element ID" and Element "Element Data Size Size" are both encoded as a Variable
   "Variable Size Integer, Integer", developed according to a UTF-8 like system.
   The
   Variable "Variable Size Integer Integer" is composed of a VINT_WIDTH, VINT_MARKER, "VINT_WIDTH",
   "VINT_MARKER", and
   VINT_DATA, "VINT_DATA", in that order.  Variable  "Variable Size Integers shall
   Integers" SHALL left-pad the "VINT_DATA" value with zero bits so that
   the whole "Variable Size Integer" is octet-aligned.  "Variable Size
   Integers" SHALL be referred to as VINT "VINT" for shorthand.

1.5.1.

5.1.  VINT_WIDTH

   Each Variable "Variable Size Integer Integer" begins with a VINT_WIDTH "VINT_WIDTH" which
   consists of zero or many zero-value bits.  The count of consecutive
   zero-values of the VINT_WIDTH "VINT_WIDTH" plus one equals the length in octets
   of the
   Variable "Variable Size Integer. Integer".  For example, a Variable "Variable Size Integer
   Integer" that starts with a VINT_WIDTH "VINT_WIDTH" which contains zero
   consecutive zero-value bits is one octet in length and a Variable "Variable
   Size Integer Integer" that starts with one consecutive zero-value bit is two
   octets in length.  The
   VINT_WIDTH "VINT_WIDTH" MUST only contain zero-value bits
   or be empty.

1.5.2.

   Within the "EBML Header" the "VINT_WIDTH" MUST NOT exceed three bits
   in length (meaning that the "Variable Size Integer" MUST NOT exceed
   four octets in length).  Within the "EBML Body", when "VINTs" are
   used to express an "Element ID", the maximum length allowed for the
   "VINT_WIDTH" is one less than the value set in the "EBMLMaxIDLength
   Element".  Within the "EBML Body", when "VINTs" are used to express
   an "Element Data Size", the maximum length allowed for the
   "VINT_WIDTH" is one less than the value set in the "EBMLMaxSizeLength
   Element".

5.2.  VINT_MARKER

   The VINT_MARKER "VINT_MARKER" serves as a separator between the VINT_WIDTH "VINT_WIDTH" and
   VINT_DATA.
   "VINT_DATA".  Each Variable "Variable Size Integer Integer" MUST contain exactly one
   VINT_MARKER.
   "VINT_MARKER".  The VINT_MARKER "VINT_MARKER" MUST be one bit in length and
   contain a bit with a value of one.  The first bit with a value of one
   within the Variable "Variable Size Integer Integer" is the VINT_MARKER.

1.5.3. "VINT_MARKER".

5.3.  VINT_DATA

   The VINT_DATA "VINT_DATA" portion of the Variable "Variable Size Integer Integer" includes all
   data that follows (but not including) the VINT_MARKER "VINT_MARKER" until end of
   the
   Variable "Variable Size Integer Integer" whose length is derived from the VINT_WIDTH.
   "VINT_WIDTH".  The bits required for the VINT_WIDTH "VINT_WIDTH" and the VINT_MARKER
   "VINT_MARKER" combined use one bit per octet out of eight bits of the total length
   of the Variable "Variable Size Integer. Integer".  Thus a Variable "Variable Size Integer Integer" of 1
   octet length supplies 7 bits for
   VINT_DATA, "VINT_DATA", a 2 octet length
   supplies 14 bits for VINT_DATA, "VINT_DATA", and a 3 octet length supplies 21
   bits for VINT_DATA. "VINT_DATA".  If the number of bits required for VINT_DATA "VINT_DATA"
   are less than the bit size of VINT_DATA, "VINT_DATA", then
   VINT_DATA may "VINT_DATA" SHOULD be
   zero-padded to the left to a size that fits.  The
   VINT_DATA "VINT_DATA" value
   MUST be expressed as a big-endian unsigned integer.

1.5.4.

5.4.  VINT Examples

   This table shows examples of Variable "Variable Size Integers at widths of Integers" with lengths
   from 1 to 5 octets.  The Size column refers to the size of the
   "VINT_DATA" in bits.  The Representation column depicts a binary
   expression of
   Variable "Variable Size Integers Integers" where VINT_WIDTH "VINT_WIDTH" is depicted
   by '0', the
   VINT_MARKER "VINT_MARKER" as '1', and the VINT_DATA "VINT_DATA" as 'x'.

   +-------------+------+----------------------------------------------+
   |    Octet Width    | Size | Representation                               |
   |    Length   |      |                                              |
   +-------------+------+----------------------------------------------+
   |      1      | 2^7  | 1xxx xxxx                                    |
   |      2      | 2^14 | 01xx xxxx xxxx xxxx                          |
   |      3      | 2^21 | 001x xxxx xxxx xxxx xxxx xxxx                |
   |      4      | 2^28 | 0001 xxxx xxxx xxxx xxxx xxxx xxxx xxxx      |
   |      5      | 2^35 | 0000 1xxx xxxx xxxx xxxx xxxx xxxx xxxx xxxx |
   |             |      | xxxx                                         |
   +-------------+------+----------------------------------------------+

   Note that data

   Data encoded as a Variable "Variable Size Integer may Integer" MAY be rendered at octet widths
   lengths larger than needed to store the data.  In this table a binary
   value of 0b10 "0b10" is shown encoded as different Variable "Variable Size
   Integers
   Integers" with widths lengths from one octet to four octet.  All four
   encoded examples have identical semantic meaning though the VINT_WIDTH
   "VINT_WIDTH" and the padding of the VINT_DATA "VINT_DATA" vary.

   +--------------+-------------+--------------------------------------+

   +--------------+--------------+-------------------------------------+
   | Binary Value | Octet Width Length | As Represented in Variable Size     |
   |              |              | Integer                             |
   +--------------+-------------+--------------------------------------+
   +--------------+--------------+-------------------------------------+
   |      10      |      1       | 1000 0010                           |
   |      10      |      2       | 0100 0000 0000 0010                 |
   |      10      |      3       | 0010 0000 0000 0000 0000 0010       |
   |      10      |      4       | 0001 0000 0000 0000 0000 0000 0000  |
   |              |              | 0010                                |
   +--------------+-------------+--------------------------------------+

1.6.
   +--------------+--------------+-------------------------------------+

6.  Element ID

   The Element ID "Element ID" MUST be encoded as a Variable "Variable Size Integer. Integer".  By
   default, EBML Element IDs may be "Element IDs" are encoded in lengths from one octet to four
   octets, although Element IDs "Element IDs" of greater lengths may be are used if the
   octet length of the EBML Document's longest Element ID "Element ID" of the "EBML Document" is
   declared in the EBMLMaxIDLength Element "EBMLMaxIDLength Element" of the EBML Header. "EBML Header" (see
   Section 11.2.4).  The
   VINT_DATA "VINT_DATA" component of the Element ID "Element ID" MUST
   NOT be set to either all zero values or all one values.  The VINT_DATA
   "VINT_DATA" component of the
   Element ID "Element ID" MUST be encoded at the
   shortest valid length.  For example, an Element ID "Element ID" with binary
   encoding of 1011 1111 "1011 1111" is valid, whereas an Element ID "Element ID" with binary
   encoding of 0100 "0100 0000 0011 1111 1111" stores a semantically equal VINT_DATA
   "VINT_DATA" but is invalid because a shorter VINT "VINT" encoding is
   possible.  Additionally, an "Element ID" with binary encoding of
   "1111 1111" is invalid since the "VINT_DATA" section is set to all
   one values, whereas an "Element ID" with binary encoding of "0100
   0000 0111 1111" stores a semantically equal "VINT_DATA" and is the
   shortest "VINT" encoding is possible.

   The following table details these specific examples further:

   +------------+-------------+----------------+-----------------------+
   | VINT_WIDTH | VINT_MARKER |      VINT_DATA | Element ID Status     |
   +------------+-------------+----------------+-----------------------+
   |            |           1 |        0000000 | Invalid: VINT_DATA    |
   |            |             |                | MUST NOT be set to    |
   |            |             |                | all 0                 |
   |          0 |           1 | 00000000000000 | Invalid: VINT_DATA    |
   |            |             |                | MUST NOT be set to    |
   |            |             |                | all 0                 |
   |            |           1 |        0000001 | Valid                 |
   |          0 |           1 | 00000000000001 | Invalid: A shorter    |
   |            |             |                | VINT_DATA encoding is |
   |            |             |                | available.            |
   |            |           1 |        0111111 | Valid                 |
   |          0 |           1 | 00000000111111 | Invalid: A shorter    |
   |            |             |                | VINT_DATA encoding is possible.  The following table details this
   specific example further:

     +------------+-------------+----------------+-------------------+ | VINT_WIDTH
   | VINT_MARKER            |      VINT_DATA             | Element ID Status                |
     +------------+-------------+----------------+-------------------+ available.            |
   |            |           1 |        0111111        1111111 | Valid Invalid: VINT_DATA    |
   |            |             |                | MUST NOT be set to    |
   |            |             |                | all 1                 |
   |          0 |           1 | 00000000111111 00000001111111 | Invalid Valid                 |
     +------------+-------------+----------------+-------------------+
   +------------+-------------+----------------+-----------------------+

   The octet length of an Element ID "Element ID" determines its EBML Class. "EBML Class".

      +------------+--------------+--------------------------------+
      | EBML Class | Octet Length | Number of Possible Element IDs |
      +------------+--------------+--------------------------------+
      |  Class A   |      1       | 2^7  - 2        =         126  |
      |  Class B   |      2       | 2^14 - 2^7  - 1 =      16,255  |
      |  Class C   |      3       | 2^21 - 2^14 - 1 =   2,080,767  |
      |  Class D   |      4       | 2^28 - 2^21 - 1 = 266,388,303 266,338,303  |
      +------------+--------------+--------------------------------+

1.7.

7.  Element Data Size

   The Element "Element Data Size Size" expresses the length in octets of Element Data. "Element
   Data".  The Element "Element Data Size Size" itself MUST be encoded as a Variable "Variable
   Size
   Integer. Integer".  By default, EBML Element "Element Data Sizes Sizes" can be encoded in
   lengths from one octet to eight octets, although Element "Element Data Sizes Sizes"
   of greater lengths MAY be used if the octet length of the EBML
   Document's longest Element
   "Element Data Size Size" of the "EBML Document" is declared in the
   EBMLMaxSizeLength Element
   "EBMLMaxSizeLength Element" of the EBML Header. "EBML Header" (see
   Section 11.2.5).  Unlike the VINT_DATA "VINT_DATA" of the Element ID, "Element ID", the VINT_DATA
   "VINT_DATA" component of the Element "Element Data Size Size" is not required mandated to
   be encoded at the shortest valid length.  For example, an Element "Element
   Data Size Size" with binary encoding of 1011 1111 "1011 1111" or a binary encoding
   of 0100 "0100 0000 0011 1111 1111" are both valid Element "Element Data
   Sizes Sizes" and both
   store a semantically equal value. value (both "0b00000000111111" and
   "0b0111111", the "VINT_DATA" sections of the examples, represent the
   integer 63).

   Although an Element ID "Element ID" with all VINT_DATA "VINT_DATA" bits set to zero is
   invalid, an Element "Element Data Size Size" with all VINT_DATA "VINT_DATA" bits set to zero
   is allowed for EBML Data Types "EBML Element Types" which do not mandate a non-zero length.
   length (see Section 8).  An Element "Element Data Size Size" with all VINT_DATA "VINT_DATA"
   bits set to zero indicates that the Element Data of the Element "Element Data" is zero octets in
   length.  Such an Element "EBML Element" is referred to as an Empty Element. "Empty Element".
   If an Empty Element "Empty Element" has a "default" value declared then that default value the "EBML
   Reader" MUST be
   interpreted as interpret the value of the Empty Element. "Empty Element" as the
   "default" value.  If an Empty Element "Empty Element" has no "default" value
   declared then the semantic meaning "EBML Reader" MUST interpret the value of Empty
   Element is the
   "Empty Element" as defined as part of the definition of the EBML
   corresponding "EBML Element
   Types. Type" associated with the "Element ID".

   An Element "Element Data Size Size" with all VINT_DATA "VINT_DATA" bits set to one is
   reserved as an indicator that the size of the Element "EBML Element" is
   unknown.  The only reserved value for the VINT_DATA "VINT_DATA" of Element "Element
   Data Size Size" is all bits set to one.  This rule  An "EBML Element" with an unknown
   "Element Data Size" is referred to as an "Unknown-Sized Element".
   Only "Master Elements" SHALL be "Unknown-Sized Elements".  "Master
   Elements" MUST NOT use an unknown size unless the
   "unknownsizeallowed" attribute of their "EBML Schema" is set to true
   (see Section 11.1.4.10).  The use of "Unknown-Sized Elements" allows
   for an Element "EBML Element" to be written and read before the size of the Element
   "EBML Element" is known; however unknown Element Data
   Size values SHOULD known.  "Unknown-Sized Element" MUST NOT be used unnecessarily.  An Element with an
   unknown Element Data Size MUST be a Master-element in that it
   contains other EBML Elements as sub-elements.  Master-elements MAY
   only use an unknown size or
   defined unnecessarily; however if the "unknownsizeallowed" attribute of the
   EBML Schema "Element Data Size" is set to true. not
   known before the "Element Data" is written, such as in some cases of
   data streaming, then "Unknown-Sized Elements" MAY be used.  The end
   of a Master-element with unknown
   size an "Unknown-Sized Element" is determined by the beginning of the
   next element element, defined by this document or the corresponding "EBML
   Schema", that is not a valid sub-element of that Master-element.  An Element with an unknown
   Element Data Size is referred to as an the "Unknown-Sized
   Element".

   For Element "Element Data Sizes Sizes" encoded at octet lengths from one to eight,
   this table depicts the range of possible values that can be encoded
   as an Element "Element Data Size. Size".  An Element "Element Data Size Size" with an octet
   length of 8 is able to express a size of 2^56-2 or
   72,057,594,037,927,934 octets (or about 72 petabytes).  The maximum
   possible value that can be stored as Element "Element Data Size Size" is referred
   to as "VINTMAX".

                  +--------------+----------------------+
                  | Octet Length | Possible Value Range |
                  +--------------+----------------------+
                  |      1       |     0 to  2^7-2      |
                  |      2       |     0 to 2^14-2      |
                  |      3       |     0 to 2^21-2      |
                  |      4       |     0 to 2^28-2      |
                  |      5       |     0 to 2^35-2      |
                  |      6       |     0 to 2^42-2      |
                  |      7       |     0 to 2^49-2      |
                  |      8       |     0 to 2^56-2      |
                  +--------------+----------------------+

   If the length of Element Data "Element Data" equals 2^(n*7)-1 "2^(n*7)-1" then the octet
   length of the Element "Element Data Size Size" MUST be at least n+1. "n+1".  This rule
   prevents an
   Element "Element Data Size Size" from being expressed as a reserved
   value.  For example, an Element "EBML Element" with an octet length of 127
   MUST NOT be encoded in an Element "Element Data Size Size" encoding with a one
   octet length.  The following table clarifies this rule by showing a
   valid and invalid expression of an Element "Element Data Size Size" with a VINT_DATA
   "VINT_DATA" of 127 (which is equal to 2^(1*7)-1).

   +------------+-------------+----------------+-----------------------+
   | VINT_WIDTH | VINT_MARKER |      VINT_DATA |   Element Data Size   |
   |            |             |                |         Status        |
   +------------+-------------+----------------+-----------------------+
   |            |           1 |        1111111 |   Reserved (meaning   |
   |            |             |                |        Unknown)       |
   |          0 |           1 | 00000001111111 |   Valid (meaning 127  |
   |            |             |                |        octets)        |
   +------------+-------------+----------------+-----------------------+

1.8.

8.  EBML Element Types

   Each

   "EBML Element" are defined EBML Element by an "EBML Schema" which MUST have a declared declare one
   of the follow "EBML Element Type.  The Types" for each "EBML Element".  An "EBML
   Element Type Type" defines a concept for of storing data within an "EBML
   Element" that may be
   constrained by describes such characteristics as length, endianness,
   and purpose.

   +------------+------------------------------------------------------+
   | Element    | Signed definition.

   "EBML Elements" which are defined as a "Signed Integer                                       |
   | Data Type  |                                                      |
   +------------+------------------------------------------------------+
   | Endianness | Big-endian                                           |
   | Length     | A Element",
   "Unsigned Integer Element", "Float Element", or "Date Element" use
   big endian storage.

8.1.  Signed Integer Element

   A "Signed Integer Element" MUST declare a length that  |
   |            | is no greater than 8 from zero to eight
   octets. An Signed  If the "EBML Element" is not defined to have a "default"
   value, then a "Signed Integer       |
   |            | Element Element" with a zero-octet length
   represents an       |
   |            | integer value of zero.                               |
   | Definition |

   A Signed "Signed Integer Element" stores an integer (meaning that it  |
   |            | can be
   written without a fractional component) which |
   |            | may could be negative,
   positive, or zero.  Signed Integers MUST be stored with two's
   complement notation with the leftmost bit being the sign bit.
   Because EBML     |
   |            | "EBML" limits Signed Integers to 8 octets in length a       |
   |            | Signed Element may store "Signed
   Ingeter Element" stores a number from               |
   |            | -9,223,372,036,854,775,808 to                        |
   |            |
   +9,223,372,036,854,775,807.                          |
   +------------+------------------------------------------------------+
   +------------+------------------------------------------------------+
   | Element    |

8.2.  Unsigned Integer                                     |
   | Data Type  |                                                      |
   +------------+------------------------------------------------------+
   | Endianness | Big-endian                                           |
   | Length     | Element

   A Unsigned "Unsigned Integer Element Element" MUST declare a length     |
   |            | that is no greater than 8 from zero to eight
   octets. An Unsigned        |
   |            |  If the "EBML Element" is not defined to have a "default"
   value, then an "Unsigned Integer Element Element" with a zero-octet length
   represents  |
   |            | an integer value of zero.                            |
   | Definition |

   An Unsigned "Unsigned Integer Element" stores an integer (meaning that  |
   |            | it can
   be written without a fractional component)    |
   |            | which may could be positive or
   zero.  Because EBML "EBML" limits   |
   |            | Unsigned Integers to 8 octets in length
   an unsigned  |
   |            | Element may store "Unsigned Integer Element" stores a number from 0 to                 |
   |            |
   18,446,744,073,709,551,615.                          |
   +------------+------------------------------------------------------+

   +------------+------------------------------------------------------+
   | Element    | Float                                                |
   | Data Type  |                                                      |
   +------------+------------------------------------------------------+
   | Endianness | Big-endian                                           |
   | Length     | A

8.3.  Float Element

   A "Float Element" MUST declare of a length of either 0   |
   |            | zero octets (0
   bit), 4 four octets (32 bit) or 8 eight octets (64    |
   |            | bit). A Float Element  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.                |
   | Definition |

   A Float Elements "Float Element" stores a floating-point number as   |
   |            | defined in IEEE 754.                                 |
   +------------+------------------------------------------------------+

   +------------+------------------------------------------------------+
   | Element    | String                                               |
   | Data Type  |                                                      |
   +------------+------------------------------------------------------+
   | Endianness | None                                                 |
   | Length     | A
   [IEEE.754.1985].

8.4.  String Element may

   A "String Element" MUST declare any a length in octets from zero to |
   |            |
   "VINTMAX".                                           |
   | Definition |  If the "EBML Element" is not defined to have a "default"
   value, then a "String Element" with a zero-octet length represents an
   empty string.

   A String Element may "String Element" MUST either be empty (zero-length)   |
   |            | or contain
   Printable ASCII characters [RFC0020] in the range   |
   |            | of 0x20 "0x20" to 0x7E.
   "0x7E".  Octets with all bits set to zero    |
   |            | may MAY follow the string value
   when needed.             |
   +------------+------------------------------------------------------+
   +------------+------------------------------------------------------+
   | Element    | UTF-8                                                |
   | needed, such as reducing the length of a stored string while
   maintaining the same "Element Data Type  |                                                      |
   +------------+------------------------------------------------------+
   | Endianness | None                                                 |
   | Length     | Size".  A string with one or more
   octets with all bits set to zero and a string without one or more
   octets with all bits set to zero are semantically equal.

8.5.  UTF-8 Element may

   A "UTF-8 Element" MUST declare any a length in octets from zero to  |
   |            |
   "VINTMAX".                                           |
   | Definition |  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.

   A UTF-8 Element shall contain "UTF-8 Element" contains only a valid Unicode   |
   |            | string as defined in RFC 2279 [2].
   [RFC2279].  Octets with all   |
   |            | bits set to zero may MAY follow the UTF-8 string
   value when     |
   |            | needed.                                              |
   +------------+------------------------------------------------------+

   +------------+------------------------------------------------------+
   | Element    | Date                                                 |
   | needed, such as reducing the length of a stored UTF-8 data
   while maintaining the same "Element Data Type  |                                                      |
   +------------+------------------------------------------------------+
   | Endianness | None                                                 |
   | Length     | Size".  A UTF-8 value with
   one or more octets with all bits set to zero and a UTF-8 value
   without one or more octets with all bits set to zero are semantically
   equal.

8.6.  Date Element

   A "Date Element" MUST declare a length of either 0     |
   |            | zero octets or 8 eight
   octets. A Date Element  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                     |
   |            | 2001-01-01T00:00:00.000000000 UTC.                   |
   | Definition | UTC [RFC3339].

   The Date Element MUST contain a Signed "Date Element" stores an integer in the same format as the
   "Signed Integer Element" that  |
   |            | expresses a point in time referenced in
   nanoseconds  |
   |            | from the precise beginning of the third millennium   |
   |            | of the
   Gregorian Calendar in Coordinated Universal   |
   |            | Time (also known as
   2001-01-01T00:00:00.000000000    |
   |            | UTC).  This provides a possible
   expression of time    |
   |            | from 1708-09-11T00:12:44.854775808 UTC to            |
   |            |
   2293-04-11T11:47:16.854775807 UTC.                   |
   +------------+------------------------------------------------------+
   +------------+------------------------------------------------------+
   |

8.7.  Master Element    | Master-element                                       |
   | Data Type  |                                                      |
   +------------+------------------------------------------------------+
   | Endianness | None                                                 |
   | Length     |

   A Master-element may "Master Element" MUST declare any a length in octets from zero to |
   |            |
   "VINTMAX".  The Master-element may "Master Element" MAY also use an        |
   |            | unknown length.  See the section on Element Data Size |
   |            |
   Section 7 for rules that apply to elements of unknown length.  |
   | Definition | The Master-element contains zero, one, or many other |
   |            | elements. Elements contained within a Master-element |
   |            | must be defined for use at levels greater than the   |
   |            | level of the Master-element. For instance is a       |
   |            | Master-element occurs on level 2 then all contained  |
   |            | Elements must be valid at level 3. Element Data      |
   |            | unknown length.

   The "Master Element" contains zero, one, or many other elements.
   "EBML Elements" contained within a "Master Element" MUST have the
   "EBMLParentPath" of their "Element Path" equals to the
   "EBMLReferencePath" of the "Master Element" "Element Path" (see
   Section 11.1.4.2).  "Element Data" stored within Master-elements "Master Elements"
   SHOULD only consist of |
   |            | EBML Elements "EBML Elements" and SHOULD NOT contain any
   data that   |
   |            | is not part of an EBML Element. "EBML Element".  When EBML "EBML" is used in |
   |            |
   transmission or streaming, data that is not part of  |
   |            | an EBML Element "EBML Element"
   is permitted to be present within a  |
   |            | Master-element "Master Element" if
   "unknownsizeallowed" is enabled    |
   |            | within the definition for that Master-element's definition.
   "Master Element".  In this     |
   |            | case, the reader "EBML Reader" should skip data
   until a valid      |
   |            | Element ID "Element ID" of the same level "EBMLParentPath" or the next greater     |
   |            |
   upper level "Element Path" of the Master-element "Master Element" is found.  What Element   |
   |            | IDs
   "Element IDs" are considered valid within a Master-element "Master Element" is  |
   |            |
   identified by the EBML Schema "EBML Schema" for that version of    |
   |            | the EBML "EBML
   Document Type. Type".  Any data contained with within a    |
   |            | Master-element "Master Element" that is
   not part of an Element SHOULD |
   |            | a "Child Element" MUST be ignored.                                          |
   +------------+------------------------------------------------------+

   +--------------+----------------------------------------------------+
   | Element Data |

8.8.  Binary                                             |
   | Type         |                                                    |
   +--------------+----------------------------------------------------+
   | Endianness   | None                                               |
   | Length       | Element

   A binary element may "Binary Element" MUST declare any a length in octets from zero  |
   |              | to
   "VINTMAX".                                      |
   | Definition   |

   The contents of a Binary element "Binary Element" should not be     |
   |              | interpreted by the EBML parser.                    |
   +--------------+----------------------------------------------------+

1.9.
   "EBML Reader".

9.  EBML Document

   An EBML Document "EBML Document" is comprised of only two components, an EBML Header "EBML
   Header" and an EBML Body. "EBML Body".  An EBML Document "EBML Document" MUST start with an EBML Header
   which
   "EBML Header" that declares significant characteristics of the entire EBML Body.
   "EBML Body".  An EBML Document MAY only consist "EBML Document" consists of EBML Elements "EBML Elements" and MUST
   NOT contain any data that is not part of an EBML Element.  The initial
   EBML Element of an EBML Document and the Elements that follow it are
   considered Level 0 Elements.  If an EBML Master-element is considered
   to be at level N and it contains one or many other EBML Elements then
   the contained Elements shall be considered at Level N+1.  Thus a
   Level 2 Element would have to be contained by a Master-element (at
   Level 1) that is contained by another Master-element (at Level 0).

1.9.1. "EBML Element".

9.1.  EBML Header

   The EBML Header "EBML Header" is a declaration that provides processing
   instructions and identification of the EBML Body. "EBML Body".  The EBML Header
   may be considered as "EBML
   Header" of an "EBML Document" is analogous to the XML Declaration of
   an XML Declaration.  All EBML
   Documents MUST begin with a valid EBML Header. Document.

   The EBML Header "EBML Header" documents the EBML Schema "EBML Schema" (also known as the EBML
   DocType)
   "EBML DocType") that may be is used to semantically interpret the structure
   and meaning of the EBML Document. "EBML Document".  Additionally the EBML Header "EBML Header"
   documents the versions of both EBML "EBML" and the EBML Schema "EBML Schema" that were
   used to write the EBML Document "EBML Document" and the versions required to read
   the EBML
   Document. "EBML Document".

   The EBML Header "EBML Header" consists of a single Master-element "Master Element" with an Element
   ID
   "Element Name" of 'EBML'. "EBML" and "Element ID" of "0x1A45DFA3" (see
   Section 11.2.1).  The EBML Header "EBML Header" MUST ONLY only contain EBML Elements "EBML Elements"
   that are defined as part of the EBML Specification. this document.

   All EBML Elements "EBML Elements" within the EBML Header "EBML Header" MUST NOT utilize use any Element
   ID
   "Element ID" with a length greater than 4 octets.  All EBML Elements "EBML
   Elements" within the
   EBML Header "EBML Header" MUST NOT utilize use any Element "Element Data Size
   Size" with a length greater than 4 octets.

1.9.2.

9.2.  EBML Body

   All data of an EBML Document "EBML Document" following the EBML Header may be
   considered "EBML Header" is the EBML Body.
   "EBML Body".  The end of the EBML Body, "EBML Body", as well as the end of the EBML Document
   "EBML Document" that contains the EBML Body, "EBML Body", is considered as
   whichever comes first: the beginning of a new level 0 EBML Header "EBML Header" at the
   "Root Level" or the end of the file.  The EBML Body MAY only "EBML Body" MUST consist
   only of EBML
   Elements "EBML Elements" and MUST NOT contain any data that is not
   part of an EBML
   Element.  Although the EBML specification itself "EBML Element".  This document defines precisely what EBML Elements
   "EBML Elements" are to be used within the EBML Header, the EBML
   specification "EBML Header", but does not
   name or define what EBML Elements "EBML Elements" are to be used within the EBML Body. "EBML
   Body".  The definition of what EBML Elements "EBML Elements" are to be used within
   the EBML Body "EBML Body" is defined by an EBML Schema.

1.10. "EBML Schema".

10.  EBML Stream

   An EBML Stream "EBML Stream" is a file that consists of one or many EBML Documents "EBML
   Documents" that are concatenated together.  An occurrence of a Level 0 EBML
   Header "EBML
   Header" at the "Root Level" marks the beginning of an EBML Document.

1.11. "EBML
   Document".

11.  Elements semantic

1.11.1.  EBML Schema

   An EBML Schema is an XML Document 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 may be considered analogous to the relationship of an XML
   Schema [3] to an XML Document [4].  An EBML Schema MUST be clearly
   associated with one or many EBML Document Types.  An

11.1.  EBML Schema must
   be expressed as well-formed XML.

   An EBML Document Type is identified
   by a unique string stored within the EBML Header element called
   DocType; for example "matroska" or "webm".

   As an XML Document, the EBML Schema MUST use "<EBMLSchema>" as the
   top level element.  The "<EBMLSchema>" element MAY contain
   "<element>" sub-elements.  Each "<element>" defines one EBML Element
   through the use of several attributes which are defined in the
   section on Section 1.11.1.1.  EBML Schemas MAY contain additional
   attributes to extend the semantics but MUST NOT conflict "EBML Schema" is an XML Document that defines the
   definitions properties,
   arrangement, and usage of "EBML Elements" that compose a specific
   "EBML Document Type".  The relationship of an "EBML Schema" to an
   "EBML Document" may be considered analogous to the "<element>" attributes defined within this
   specification.

   Within the EBML relationship of an
   XML Schema each EBML Element is defined [W3C.REC-xmlschema-0-20010502] to occur at an XML Document
   [W3C.REC-xml-20081126].  An "EBML Schema" MUST be clearly associated
   with one or many "EBML Document Types".  An "EBML Schema" must be
   expressed as well-formed XML.  An "EBML Document Type" is identified
   by a
   specific level. string stored within the "EBML Header" in the "DocType Element";
   for example "matroska" or "webm" (see Section 11.2.6).  The "DocType"
   value for an "EBML Document Type" SHOULD be unique and persistent.

   For any specificied EBML Element specified "EBML Element" that is not at
   level 0, "Root Level", the Parent EBML Element
   "Parent Element" refers to the EBML Master-element
   that "Master Element" in which that EBML Element "EBML
   Element" is contained within. contained.  For any specifiied EBML
   Master-element specified "Master Element" the Child EBML Element "Child
   Element" refers to the EBML Elements "EBML Element" that may be is immediately contained
   within that Master-element. "Master Element".  For any EBML Element "EBML Element" that is not
   defined at level 0, "Root Level", the Parent EBML
   Element may be "Parent Element" is identified by the preceding
   "<element>" node which has
   a lower value as the defined "level" attribute. "EBMLReferencePath" equals to the
   "EBMLParentPath" of that "EBML Element" "Element Path".  The only
   exception for this rule are Global EBML Elements "Global Elements" which may MAY occur within
   any
   Parent EBML Element "Parent Element" within the restriction of the Global EBML
   Element's range declaration. "level"
   declaration of "Global Element".

   An EBML Schema "EBML Schema" MUST declare exactly one Element "EBML Element" at Level 0 "Root
   Level" (referred to as the Root Element) "Root Element") that MUST occur exactly
   once within an EBML
   Document. "EBML Document".  The Root Element MUST be mandatory (with minOccurs set to
   1) and MUST be defined to occur exactly once (maxOccurs set to 1).
   Note that the EBML and Void Elements may "Void Element" MAY also occur at Level 0
   "Root Level" but
   are is not considered to be Root Elements.

   Elements "Root Elements" (see
   Section 11.3.1).

   "EBML Elements" defined to only occur at Level 1 are known as Top-Level
   Elements. "Top-
   Level Elements".

   The EBML Schema "EBML Schema" does not itself document the EBML Header, "EBML Header", but
   documents all data of the EBML Document "EBML Document" that follows the EBML Header. "EBML
   Header".  The EBML Header "EBML Header" itself is documented by this
   specification in the "EBML Header Elements" (see Section 1.11.2 section. 11.2).  The EBML Schema
   "EBML Schema" also does not document
   Global Elements "Global Elements" that are
   defined by the EBML Specification this document (namely
   Void the "Void Element" and CRC-32).

1.11.1.1.  EBML Schema the "CRC-32
   Element").

11.1.1.  Element

   As an XML Document, the "EBML Schema" MUST use "<EBMLSchema>" as the
   top level element.  The "<EBMLSchema>" element MAY contain
   "<element>" sub-elements.

11.1.2.  Attributes

   Within an EBML Schema an "EBML Schema" the "<EBMLSchema>" element uses the following
   attributes to define the EBML Schema:

   +-----------+----------+--------------------------------------------+
   | attribute | required | definition                                 |
   | name      |          |                                            |
   +-----------+----------+--------------------------------------------+
   |
   attributes:

11.1.2.1.  docType   | Yes      |

   The "docType" lists the official name of   |
   |           |          | the EBML "EBML Document Type Type"
   that is defined by  |
   |           |          | the EBML Schema; "EBML Schema"; for example, "<EBMLSchema |
   |           |          |
   docType="matroska">".                      |
   |

   The "docType" attribute is REQUIRED within the "<EBMLSchema>"
   Element.

11.1.2.2.  version   | Yes      |

   The "version" lists an incremental non-    |
   |           |          | negative non-negative integer that
   specifies the        |
   |           |          | version of the docType documented by the   |
   |           |          | EBML Schema. "EBML Schema".
   Unlike XML Schemas, an EBML   |
   |           |          | Schema "EBML Schema" documents all versions of a         |
   |           |          |
   docType's definition rather than using     |
   |           |          | separate EBML Schemas "EBML Schemas" for
   each version of  |
   |           |          | a docType. Elements "docType".  "EBML Elements" may be introduced and  |
   |           |          |
   deprecated by using the "minver" and       |
   |           |          | "maxver" attributes of .                   |
   +-----------+----------+--------------------------------------------+
   "<element>".

   The "version" attribute is REQUIRED within the "<EBMLSchema>"
   Element.

11.1.3.  Element

   Each "<element>" defines one "EBML Element" through the use of
   several attributes that are defined in Section 11.1.2.  "EBML
   Schemas" MAY contain additional attributes to extend the semantics
   but MUST NOT conflict with the definitions of the "<element>"
   attributes defined within this document.

   The "<element>" nodes contain a description of the meaning and use of
   the "EBML Element" stored within one or many "<documentation>" sub-
   elements.  All "<element>" nodes MUST be sub-elements of the
   "<EBMLSchema>".

11.1.4.  Attributes

   Within an EBML Schema "EBML Schema" the "<element>" uses the following attributes
   to define an EBML Element.

   +--------------------+----------+-----------------------------------+
   | attribute name     | required | definition                        |
   +--------------------+----------+-----------------------------------+
   | "EBML Element":

11.1.4.1.  name               | Yes      |

   The "name" provides the official human-readable name  |
   |                    |          | of the EBML Element. "EBML
   Element".  The value of |
   |                    |          | the name MUST be in the form of   |
   |                    |          | an NCName as defined by the XML   |
   |                    |          | Schema specification [5].         |
   | level              | Yes      | characters
   "A" to "Z", "a" to "z", "0" to "9", "-" and ".".

   The level notes at what           |
   |                    |          | hierarchical depth "name" attribute is REQUIRED.

11.1.4.2.  path

   The path defines the EBML       |
   |                    |          | Element may occur allowed storage locations of the "EBML Element"
   within an EBML  |
   |                    |          | Document. "EBML Document".  This path MUST be defined with the full
   hierarchy of "EBML Elements" separated with a "/".  The Root Element top "EBML
   Element" in the path hierarchy being the first in the value.  The
   syntax of an  |
   |                    |          | EBML Document the "path" attribute is at level 0 and   |
   |                    |          | defined using this Augmented
   Backus-Naur Form (ABNF) [RFC5234] with the Elements that it may contain  |
   |                    |          | are at level 1. case sensitive update
   [RFC7405] notation:

   The level "path" attribute is REQUIRED.

EBMLFullPath            = EBMLElementOccurence "(" EBMLReferencePath ")"
EBMLReferencePath       = [EBMLParentPath] EBMLElementPath
EBMLParentPath          = EBMLFixedParent EBMLLastParent
EBMLFixedParent         = *(EBMLPathAtom)
EBMLElementPath         = EBMLPathAtom / EBMLPathAtomRecursive
EBMLPathAtom            = PathDelimiter EBMLAtomName
EBMLPathAtomRecursive   = "1*(" EBMLPathAtom ")"
EBMLLastParent          = EBMLPathAtom / EBMLVariableParent
EBMLVariableParent      = "(" VariableParentOccurence "\)"
EBMLAtomName            = 1*(EBMLNameChar)
EBMLNameChar            = ALPHA / DIGIT / "-" / "."
PathDelimiter           = "\"
EBMLElementOccurence    = [EBMLMinOccurence] "*" [EBMLMaxOccurence]
EBMLMinOccurence        = 1*DIGIT
EBMLMaxOccurence        = 1*DIGIT
VariableParentOccurence = [PathMinOccurence] "*" [PathMaxOccurence]
PathMinOccurence        = 1*DIGIT
PathMaxOccurence        = 1*DIGIT

   The ""*"", ""("" and "")"" symbols MUST be |
   |                    |          | expressed interpreted as an integer. Note     |
   |                    |          | that Elements they are
   defined as "global" |
   |                    |          | and "recursive" MAY occur at a    |
   |                    |          | level greater than or in the ABNF.

   The "EBMLPathAtom" part of the "EBMLElementPath" MUST be equal to    |
   |                    |          | the defined "level".              |
   | global             | No       | A boolean
   "name" attribute of the "EBML Schema".

   The starting "PathDelimiter" of the path corresponds to express if an EBML   |
   |                    |          | Element MUST occur at its defined |
   |                    |          | level or may occur within any     |
   |                    |          | Parent EBML Element. If the       |
   |                    |          | "global" attribute is not         |
   |                    |          | expressed for that Element then   |
   |                    |          | that element root of
   the "EBML Document".

   The "EBMLElementOccurence" part is interpreted as an ABNF Variable
   Repetition.  The repetition amounts correspond to how many times the
   "EBML Element" can be considered  |
   |                    |          | not global.                       |
   | id                 | Yes      | The Element ID expressed found in       |
   |                    |          | hexadecimal notation prefixed by  |
   |                    |          | a '0x'. To reduce its parent "Parent Element".

   The "EBMLMinOccurence" represents the risk minimum number of     |
   |                    |          | false positives while parsing     |
   |                    |          | EBML Streams, the IDs occurrences
   of this "EBML Element" within its "Parent Element".  Each instance of
   the Root |
   |                    |          | Element and Top-Level Elements    |
   |                    |          | SHOULD be "Parent Element" MUST contain at least 4 octets in    |
   |                    |          | length. Element IDs defined for   |
   |                    |          | use at Level 0 or Level 1 MAY use |
   |                    |          | shorter octet lengths this many instances of
   this "EBML Element".  If the "EBML Element" has an empty
   "EBMLParentPath" then "EBMLMinOccurence" refers to          |
   |                    |          | facilitate padding and optimize   |
   |                    |          | edits constaints on the
   occurrence of the "EBML Element" within the "EBML Document".  If
   "EBMLMinOccurence" is not present then that "EBML Element" is
   considered to have a "EBMLMinOccurence" value of 0.  The semantic
   meaning of "EBMLMinOccurence" within an "EBML Schema" is considered
   analogous to EBML Documents; for      |
   |                    |          | instance, the EBML Void Element   |
   |                    |          | uses meaning of "minOccurs" within an Element ID "XML Schema".
   "EBML Elements" with "EBMLMinOccurence" set to "1" that also have a one     |
   |                    |          | octet length
   "default" value (see Section 11.1.4.8) declared are not REQUIRED to allow its usage   |
   |                    |          | in more writing and editing       |
   |                    |          | scenarios.                        |
   | minOccurs          | No       | An integer
   be stored but are REQUIRED to express the minimal |
   |                    |          | number of occurrences that the    |
   |                    |          | be interpreted, see Section 11.1.11.
   An "EBML Element" defined with a "EBMLMinOccurence" value greater
   than zero is called a "Mandatory EBML Element MUST occur within    |
   |                    |          | its Parent Element if Element".

   The "EBMLMaxOccurence" represents the maximum number of occurrences
   of this "EBML Element" within its Parent  |
   |                    |          | Element is used. "Parent Element".  Each instance of
   the "Parent Element" MUST contain at most this many instances of this
   "EBML Element".  If the Element   |
   |                    |          | "EBML Element" has no Parent Level (as is the    |
   |                    |          | case with Elements at Level 0),   |
   |                    |          | an empty "EBMLParentPath"
   then minOccurs "EBMLMaxOccurence" refers to          |
   |                    |          | constaints on the Element's       |
   |                    |          | occurrence of the
   "EBML Element" within the EBML        |
   |                    |          | Document. "EBML Document".  If the minOccurs        |
   |                    |          | attribute "EBMLMaxOccurence" is
   not expressed for    |
   |                    |          | that Element present then that Element    |
   |                    |          | shall be "EBML Element" is considered to have a     |
   |                    |          | minOccurs value of 0. This value  |
   |                    |          | of minOccurs MUST be a positive   |
   |                    |          | integer. an
   unbounded "EBMLMaxOccurence" value.  The semantic meaning of  |
   |                    |          | minOccurs
   "EBMLMaxOccurence" within an EBML "EBML Schema   |
   |                    |          | path" is considered
   analogous to the    |
   |                    |          | meaning of minOccurs "maxOccurs" within an    |
   |                    |          | XML Schema [6]. Note that         |
   |                    |          | Elements with minOccurs set "XML Schema".

   The "VariableParentOccurence" part is interpreted as an ABNF Variable
   Repetition.  The repetition amounts correspond to    |
   |                    |          | "1" that also have the amount of
   unspecified "Parent Element" levels there can be between the
   "EBMLFixedParent" and the actual "EBMLElementPath".

   If the path contains a default      |
   |                    |          | value declared are not required   |
   |                    |          | "EBMLPathAtomRecursive" part, the "EBML
   Element" can occur within itself recursively (see the
   Section 11.1.4.11).

11.1.4.3.  id

   The "Element ID" encoded as a "Variable Size Integer" expressed in
   hexadecimal notation prefixed by a "0x" that is read and stored in
   big-endian order.  To reduce the risk of false positives while
   parsing "EBML Streams", the "Element IDs" of the "Root Element" and
   "Top-Level Elements" SHOULD be at least 4 octets in length.  "Element
   IDs" defined for use at "Root Level" or directly under the "Root
   Level" MAY use shorter octet lengths to be stored but are required facilitate padding and
   optimize edits to  |
   |                    |          | be interpretted, see EBML Documents; for instance, the Section  |
   |                    |          | 1.11.1.6.                         |
   | maxOccurs          | No       | A value "Void Element"
   uses an "Element ID" with a one octet length to express allow its usage in
   more writing and editing scenarios.

   The "id" attribute is REQUIRED.

11.1.4.4.  minOccurs

   An integer expressing the maximum    |
   |                    |          | minimum number of occurrences that the    |
   |                    |          | EBML Element MAY occur of this "EBML
   Element" within its |
   |                    |          | Parent Element if its Parent      |
   |                    |          | Element "Parent Element".  The "minOccurs" value MUST be
   equal to the "EBMLMinOccurence" value of the "path".

   The "minOccurs" attribute is used. OPTIONAL.  If the Element   |
   |                    |          | has no Parent Level (as "minOccurs" attribute
   is the    |
   |                    |          | case with Elements at Level 0),   |
   |                    |          | not present then maxOccurs refers that "EBML Element" is considered to          |
   |                    |          | constaints on the Element's       |
   |                    |          | occurrence within the EBML        |
   |                    |          | Document. This value may be       |
   |                    |          | either have a positive
   "minOccurs" value of 0.

11.1.4.5.  maxOccurs

   An integer or expressing the  |
   |                    |          | term "unbounded" to indicate      |
   |                    |          | there is no maximum number of     |
   |                    |          | occurrences or the term           |
   |                    |          | "identical" of this "EBML
   Element" within its "Parent Element".  The "maxOccurs" value MUST be
   equal to indicate that the  |
   |                    |          | Element "EBMLMaxOccurence" value of the "path".

   The "maxOccurs" attribute is an Section 1.11.1.3.   |
   |                    |          | OPTIONAL.  If the maxOccurs "maxOccurs" attribute
   is not |
   |                    |          | expressed for that Element then   |
   |                    |          | not present then that Element shall be "EBML Element" is considered  |
   |                    |          | to have a
   maxOccurs value of 1.   |
   |                    |          | The semantic meaning of maxOccurs |
   |                    |          | within an EBML Schema is          |
   |                    |          | considered analogous to the       |
   |                    |          | meaning of minOccurs within an    |
   |                    |          | XML Schema [7], with EBML Schema  |
   |                    |          | adding the concept of Identically |
   |                    |          | Recurring Elements.               |
   |

11.1.4.6.  range              | No       | For Elements

   A numerical range for "EBML Elements" which are of         |
   |                    |          | numerical types
   (Unsigned         |
   |                    |          | Integer, Signed Integer, Float,   |
   |                    |          | and Date) a numerical range may   |
   |                    |          | be specified. Date).  If specified that   |
   |                    |          |
   the value of the EBML Element     |
   |                    |          | MUST be within the defined range  |
   |                    |          | inclusively. range.  See the
   Section      |
   |                    |          | 1.11.1.4 11.1.9 for rules applied to     |
   |                    |          | expression of range values.       |
   | default            | No       |

   The "range" attribute is OPTIONAL.  If the "range" attribute is not
   present then any value legal for the "type" attribute is valid.

11.1.4.7.  size

   A default value may to express the valid length of the "Element Data" as written
   measured in octets.  The "size" provides a constraint in addition to
   the Length value of the definition of the corresponding "EBML Element
   Type".  This "size" MUST be provided.  |
   |                    |          | expressed as either a non-negative
   integer or a range (see Section 11.1.9) that consists of only non-
   negative integers and valid operators.

   The "size" attribute is OPTIONAL.  If the "size" attribute is not
   present for that "EBML Element" then that "EBML Element" is only
   limited in size by the definition of the associated "EBML Element
   Type".

11.1.4.8.  default

   If an Element is mandatory (has a "EBMLMinOccurence" value greater
   than zero) but    |
   |                    |          | not written within its Parent     |
   |                    |          | EBML Element, then the parser of  |
   |                    |          | "Parent Element" or stored as
   an "Empty Element", then the EBML Document "EBML Reader" of the "EBML Document"
   MUST insert semantically interpret the |
   |                    |          | defined "EBML Element" as present with this
   specified default value of for the      |
   |                    |          | Element. EBML Elements "EBML Element".  "EBML Elements" that
   are   |
   |                    |          | Master-elements "Master Elements" MUST NOT declare  |
   |                    |          | a default "default" value.                  |
   | type               | Yes      | As defined within the Section     |
   |                    |          | 1.8, the

   The "default" attribute is OPTIONAL.

11.1.4.9.  type

   The "type" MUST be set to one  |
   |                    |          | of the following values:          |
   |                    |          | 'integer'
   (signed integer),       |
   |                    |          | 'uinteger' (unsigned integer),    |
   |                    |          | 'float', 'string',
   'date',        |
   |                    |          | 'utf-8', 'master', or 'binary'.   |
   |  The content of each "type"
   is defined within Section 8.

   The "type" attribute is REQUIRED.

11.1.4.10.  unknownsizeallowed | No       |

   A boolean to express if an EBML   |
   |                    |          | Element "EBML Element" MAY be used as an         |
   |                    |          | "Unknown-Sized "Unknown-
   Sized Element" (having   |
   |                    |          | all VINT_DATA "VINT_DATA" bits of Element     |
   |                    |          | "Element Data Size Size"
   set to 1).  "EBML Elements" that are not "Master Elements" MUST NOT
   set "unknownsizeallowed" to true.

   The          |
   |                    |          | "unknownsizeallowed" attribute    |
   |                    |          | only applies to Master-elements.  |
   |                    |          | is OPTIONAL.  If the
   "unknownsizeallowed"       |
   |                    |          | attribute is not used it is       |
   |                    |          | assumed then that the element "EBML Element"
   is not   |
   |                    |          | allowed to use an unknown Element |
   |                    |          | "Element Data Size.                        |
   | Size".

11.1.4.11.  recursive          | No       |

   A boolean to express if an EBML   |
   |                    |          | Element "EBML Element" MAY be stored             |
   |                    |          | recursively.
   In this case the     |
   |                    |          | Element "EBML Element" MAY be stored at levels   |
   |                    |          | greater that
   defined in the       |
   |                    |          | "level" attribute if the Element  |
   |                    |          | "EBML Element" is a Child Element "Child
   Element" of a Parent    |
   |                    |          | Element "Parent Element" with the same Element ID. |
   |                    |          | The "Element ID".  "EBML
   Elements" that are not "Master Elements" MUST NOT set "recursive" attribute only    |
   |                    |          | applies to Master-elements.
   true.

   If    |
   |                    |          | the "path" contains a "EBMLPathAtomRecursive" part then the
   "recursive" attribute is not  |
   |                    |          | used it value MUST be true and false otherwise.

   The "recursive" attribute is assumed that OPTIONAL.  If the       |
   |                    |          | element "recursive" attribute
   is not allowed to present then the "EBML Element" MUST NOT be used |
   |                    |          | recursively.                      |
   |

11.1.4.12.  minver             | No       |

   The "minver" (minimum version)    |
   |                    |          | attribute stores a non-negative   |
   |                    |          |
   integer that represents the first |
   |                    |          | version of the docType "docType" to support |
   |                    |          |
   the element. "EBML Element".

   The "minver" attribute is OPTIONAL.  If the "minver"      |
   |                    |          | attribute is not used it is       |
   |                    |          | assumed that
   present then the element "EBML Element" has a    |
   |                    |          | minimum version of "1".           |
   |

11.1.4.13.  maxver             | No       |

   The "maxver" (maximum version)    |
   |                    |          | attribute stores a non-negative   |
   |                    |          |
   integer that represents the last  |
   |                    |          | or most recent version of the     |
   |                    |          | docType
   "docType" to support the element.   |
   |                    |          | "maxver" MUST be greater than or
   equal to "minver".

   The "maxver" attribute is OPTIONAL.  If the "maxver" attribute is not  |
   |                    |          | used it is assumed that
   present then the       |
   |                    |          | element "EBML Element" has a maximum version     |
   |                    |          | equal to the
   value stored in the  |
   |                    |          | "version" attribute of .          |
   +--------------------+----------+-----------------------------------+

   The "<element>" nodes shall contain a description of the meaning and
   use of the EBML

11.1.5.  Element stored within one or many "<documentation>"
   sub-elements.

   The "<documentation>" sub-element may use a element provides additional information about
   the "EBML Element".

11.1.6.  Attributes

11.1.6.1.  lang

   A "lang" attribute which may be is set to the RFC 5646 [RFC5646] value of the
   language of the element's documentation.

   The "<documentation>" sub-element may
   use a "lang" attribute is OPTIONAL.

11.1.6.2.  type

   A "type" attribute to distinguish distinguishes the meaning of the documentation.  Recommended values
   Values for the "<documentation>" sub-
   element's sub-element's "type" attribute include: MUST
   include one of the following: "definition", "rationale", "usage
   notes", and "references".

   The "<element>" nodes MUST be arranged hierarchically according to
   the permitted structure of the EBML Document Type.  An "<element>"
   node that defines an EBML Element which is a Child Element of another
   Parent Element MUST be stored as an immediate sub-element of the
   "<element>" node that defines the Parent Element. "<element>" nodes
   that define Level 0 Elements and Global Elements should be sub-
   elements of "<EBMLSchema>".

1.11.1.2. and "references".

   The "type" attribute is OPTIONAL.

11.1.7.  EBML Schema Example
<?xml version="1.0" encoding="utf-8"?>
<EBMLSchema docType="files-in-ebml-demo" version="1">
 <!-- Root Element-->
 <element name="Files" level="0" path="*1(\Files)" id="0x1946696C" type="master">
  <documentation lang="en" type="definition">Container of data and
  attributes representing one or many files.</documentation>
 </element>
 <element name="File" level="1" path="1*(\Files\File)" id="0x6146" type="master" minOccurs="1"
  maxOccurs="unbounded">
  <documentation lang="en" type="definition">An attached file.
   </documentation> file.</documentation>
 </element>
 <element name="FileName" level="2" path="1*1(\Files\File\FileName)" id="0x614E" type="utf-8"
   minOccurs="1">
  <documentation lang="en" type="definition">Filename of the attached
    file.</documentation> file.
  </documentation>
 </element>
 <element name="MimeType" level="2" path="1*1(\Files\File\MimeType)" id="0x464D" type="string"
     minOccurs="1">
  <documentation lang="en" type="definition">MIME type of the file.</documentation>
 </element>
 <element name="ModificationTimestamp" level="2" path="1*1(\Files\File\ModificationTimestamp)"
  id="0x4654" type="date" minOccurs="1">
  <documentation lang="en" type="definition">Modification timestamp of the file.</documentation> file.
  </documentation>
 </element>
 <element name="Data" level="2" path="1*1(\Files\File\Data)" id="0x4664" type="binary"
     minOccurs="1">
  <documentation lang="en" type="definition">The data of the file.</documentation>
 </element>
  </element>
 </element>
</EBMLSchema>

1.11.1.3.

11.1.8.  Identically Recurring Elements

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

1.11.1.4.

11.1.9.  Expression of range

   The "range" attribute MUST only be used with EBML Elements that are
   either "signed integer", "unsigned integer", "float", or "float".  The "range"
   attribute does not support date EBML Elements. "date".  The
   "range" expression may contain whitespace for readability but
   whitespace within a "range" expression MUST NOT convey meaning.  The
   expression of the "range" MUST adhere to one of the following forms:

   o  "x-y" where x and y are integers or floats and "y" must MUST be greater
      than "x", meaning that the value must MUST be greater than or equal to
      "x" and less than or equal to "y". "x" MUST be less than "y".

   o  ">x" where "x" is an integer or float, meaning that the value MUST
      be greater than "x".

   o  ">=x" where "x" is an integer or float, meaning that the value
      MUST be greater than or equal to "x".

   o  "<x" where "x" is an integer or float, meaning that the value MUST
      be less than "x".

   o  "<=x" where "x" is an integer or float, meaning that the value
      MUST be less than or equal to "x".

   o  "x" where "x" is an integer or float, meaning that the value MUST
      be equal "x".

   The "range" may use the prefix "not" to indicate that the expressed
   range is negated.  Please also see the section on Section 1.11.1.5.

1.11.1.5. 11.1.10.

11.1.10.  Textual expression of Floats

   When a float value is represented textually in an EBML Schema, "EBML Schema", such
   as within a "default" or "range" value, the float values MUST be
   expressed as a Hexadecimal Floating-Point Constants as defined in the
   C11 standard ISO/IEC 9899:2011 [8] [ISO.9899.2011] (see section 6.4.4.2 on Floating
   Constants).  The following table provides examples of expressions of
   float ranges.

      +-------------------+-----------------------------------------+
      | as decimal        | as Hexadecimal Floating-Point Constants |
      +-------------------+-----------------------------------------+
      | 0.0-1.0           | 0x0p+1-0x1p+0 "0x0p+1-0x1p+0"                         |
      | 1.0-256.0         | 0x1p+0-0x1p+8 "0x1p+0-0x1p+8"                         |
      | 0.857421875       | 0x1.b7p-1 "0x1.b7p-1"                             |
      | -1.0--0.857421875 | -0x1p+0--0x1.b7p-1 "-0x1p+0--0x1.b7p-1"                    |
      +-------------------+-----------------------------------------+

   Within an expression of a float range, as in an integer range, the
   "-" (hyphen) character is the separator between the minimal and
   maximum value permitted by the range.  Note that  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 which 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 minimal and maximum value permitted by the
   range.

1.11.1.6.

11.1.11.  Note on the Use of default attributes to define Mandatory EBML
          Elements

   If a Mandatory "Mandatory EBML Element Element" has a default value declared by an EBML
   Schema
   "EBML Schema" and the EBML Element's value of the "EBML Element" is equal to the
   declared default value then that Element "EBML Element" is not required to be
   present within the EBML
   Document "EBML Document" if its Parent EBML Element "Parent Element" is
   present.  In this case, the default value of the Mandatory "Mandatory EBML Element may
   Element" MUST be assumed interpreted by the "EBML Reader" although the EBML Element "EBML
   Element" is not present within its Parent EBML Element.  Also
   in this case the parser of the EBML Document MUST insert the defined
   default value of the Element. "Parent Element".

   If a Mandatory "Mandatory EBML Element Element" has no default value declared by an EBML
   Schema
   "EBML Schema" and its Parent EBML Element "Parent Element" is present than then the EBML Element
   must "EBML
   Element" MUST be present as well.  If a Mandatory "Mandatory EBML Element Element" has
   a default value declared by an EBML Schema "EBML Schema" and its Parent EBML Element "Parent Element"
   is present and the EBML Element's value of the "EBML Element" is NOT equal to the
   declared default value then the EBML Element "EBML Element" MUST be used. present.

   This table clarifies if a Mandatory "Mandatory EBML Element Element" MUST be written,
   according to if the default "default" value is declared, if the value of the
   EBML Element
   "EBML Element" is equal to the declared default "default" value, and if the
   Parent EBML Element
   "Parent Element" is used.

   +---------------+----------------+--------------+-------------------+

   +---------------+---------------+---------------+-------------------+
   |     Is the    |  Is the value | Is the Parent |  Then is storing  |
   | default value |    equal to   |    Parent    Element    |  the EBML Element |
   |   declared?   |    default?   |   Element    |     required?     |
   |               |    present?   |    used?     REQUIRED?     |                   |
   +---------------+----------------+--------------+-------------------+
   +---------------+---------------+---------------+-------------------+
   |      Yes      |      Yes      |      Yes      |         No        |
   |      Yes      |      Yes      |       No      |         No        |
   |      Yes      |       No      |      Yes      |        Yes        |
   |      Yes      |       No      |       No      |         No        |
   |       No      |      n/a      |      Yes      |        Yes        |
   |       No      |      n/a      |       No      |         No        |
   |       No      |      n/a       |     Yes      |        Yes        |
   |       No      |      n/a       |      No      |         No        |
   +---------------+----------------+--------------+-------------------+

1.11.1.7.  Note on the Use of default attributes to define non-Mandatory
           EBML Elements

   If an EBML Element is not Mandatory, has a defined default value, and
   is an Empty EBML Element then the EBML Element MUST be interpreted as
   expressing the default value.

1.11.2.
   +---------------+---------------+---------------+-------------------+

11.2.  EBML Header Elements

   This specification here document contains definitions of all EBML Elements "EBML Elements" of the EBML Header.

   +-------------+-----------------------------------------------------+
   | Name        | EBML                                                |
   +-------------+-----------------------------------------------------+
   | Level       | 0                                                   |
   | EBML ID     | [1A][45][DF][A3]                                    |
   | Mandatory   | Yes                                                 |
   | Multiple    | No                                                  |
   | Range       | -                                                   |
   | Default     | -                                                   |
   | Type        | Master-element                                      |
   | Description |
   "EBML Header".

11.2.1.  EBML Element

   name: "EBML"

   path: "1*1(\EBML)"

   id: "0x1A45DFA3"

   minOccurs: 1

   maxOccurs: 1

   type: "Master Element"

   description: Set the EBML "EBML" characteristics of the data to follow. |
   |             |
   Each EBML Document "EBML Document" has to start with this.          |
   +-------------+-----------------------------------------------------+
   +-------------+-----------------------------------------------------+
   | Name        |

11.2.2.  EBMLVersion                                         |
   +-------------+-----------------------------------------------------+
   | Level       | Element

   name: "EBMLVersion"

   path: "1*1(\EBML\EBMLVersion)"

   id "0x4286"

   minOccurs: 1                                                   |
   | EBML ID     | [42][86]                                            |
   | Mandatory   | Yes                                                 |
   | Multiple    | No                                                  |
   | Range       |

   maxOccurs: 1                                                   |
   | Default     |

   range: 1                                                   |
   | Type        |
   default: 1

   type: Unsigned Integer                                    |
   | Description |

   description: The version of EBML parser "EBML Writer" used to create the EBML  |
   |             | Document.                                           |
   +-------------+-----------------------------------------------------+

   +-------------+-----------------------------------------------------+
   | Name        | "EBML
   Document".

11.2.3.  EBMLReadVersion                                     |
   +-------------+-----------------------------------------------------+
   | Level       | Element

   name: "EBMLReadVersion"

   path: "1*1(\EBML\EBMLReadVersion)"

   id: "0x42F7"

   minOccurs: 1                                                   |
   | EBML ID     | [42][F7]                                            |
   | Mandatory   | Yes                                                 |
   | Multiple    | No                                                  |
   | Range       |

   maxOccurs: 1                                                   |
   | Default     |

   range: 1                                                   |
   | Type        |

   default: 1

   type: Unsigned Integer                                    |
   | Description |

   description: The minimum EBML "EBML" version a parser has to support to |
   |             | read this EBML Document.                            |
   +-------------+-----------------------------------------------------+

   +-------------+-----------------------------------------------------+
   | Name        | EBMLMaxIDLength                                     |
   +-------------+-----------------------------------------------------+
   | Level       | 1                                                   |
   | EBML ID     | [42][F2]                                            |
   | Mandatory   | Yes                                                 |
   | Multiple    | No                                                  |
   | Range       | >3                                                  |
   | Default     | an "EBML Reader" has to
   support to read this "EBML Document".  The "EBMLReadVersion Element"
   MUST be less than or equal to "EBMLVersion".

11.2.4.  EBMLMaxIDLength Element

   name: "EBMLMaxIDLength"

   path: "1*1(\EBML\EBMLMaxIDLength)"

   id "0x42F2"

   minOccurs: 1

   maxOccurs: 1

   range: >=4

   default: 4                                                   |
   | Type        |

   type: Unsigned Integer                                    |
   | Description |
   description: The EBMLMaxIDLength is "EBMLMaxIDLength Element" stores the maximum length
   in octets |
   |             | of the Element IDs "Element IDs" to be found within the EBML      |
   |             | Body. "EBML Body".
   An EBMLMaxIDLength "EBMLMaxIDLength Element" value of four is           |
   |             | recommended, RECOMMENDED, though
   larger values are allowed.      |
   +-------------+-----------------------------------------------------+
   +-------------+-----------------------------------------------------+
   | Name        |

11.2.5.  EBMLMaxSizeLength                                   |
   +-------------+-----------------------------------------------------+
   | Level       | Element

   name: "EBMLMaxSizeLength"

   path: "1*1(\EBML\EBMLMaxSizeLength)"

   id "0x42F3"

   minOccurs: 1                                                   |
   | EBML ID     | [42][F3]                                            |
   | Mandatory   | Yes                                                 |
   | Multiple    | No                                                  |
   | Range       | >0                                                  |
   | Default     |

   maxOccurs: 1

   range: not 0

   default: 8                                                   |
   | Type        |

   type: Unsigned Integer                                    |
   | Description |

   description: The EBMLMaxSizeLength is "EBMLMaxSizeLength Element" stores the maximum
   length in      |
   |             | octets of the expression of all Element "Element Data Sizes  |
   |             | Sizes" to be
   found within the EBML Body. "EBML Body".  To be clear       |
   |             | EBMLMaxSizeLength the "EBMLMaxSizeLength
   Element" documents the maximum 'length' of |
   |             | all Element "Element Data Size Size"
   expressions within the EBML   |
   |             | Body "EBML Body" and not the maximum 'value' of all Element     |
   |             |
   "Element Data Size Size" expressions within the EBML Body.         |
   |             | Elements "EBML Body".  "EBML
   Elements" that have a Element an "Element Data Size Size" expression   |
   |             | which is larger
   in octets than what is expressed by |
   |             | EBMLMaxSizeLength "EBMLMaxSizeLength ELEMENT" SHALL
   be considered invalid.      |
   +-------------+-----------------------------------------------------+

   +-------------+-----------------------------------------------------+
   | Name        |

11.2.6.  DocType                                             |
   +-------------+-----------------------------------------------------+
   | Level       | Element

   name: "DocType"

   path: "1*1(\EBML\DocType)"

   id "0x4282"

   minOccurs: 1                                                   |
   | EBML ID     | [42][82]                                            |
   | Mandatory   | Yes                                                 |
   | Multiple    | No                                                  |
   | Range       | -                                                   |
   | Default     | matroska                                            |
   | Type        |

   maxOccurs: 1

   size: >0

   type: String                                              |
   | Description |
   description: A string that describes and identifies the content  |
   |             | of
   the EBML Body "EBML Body" that follows this EBML Header.     |
   +-------------+-----------------------------------------------------+
   +-------------+-----------------------------------------------------+
   | Name        | "EBML Header".

11.2.7.  DocTypeVersion                                      |
   +-------------+-----------------------------------------------------+
   | Level       | Element

   name: "DocTypeVersion"

   path: "1*1(\EBML\DocTypeVersion)"

   id "0x4287"

   minOccurs: 1                                                   |
   | EBML ID     | [42][87]                                            |
   | Mandatory   | Yes                                                 |
   | Multiple    | No                                                  |
   | Range       | -                                                   |
   | Default     |

   maxOccurs: 1                                                   |
   | Type        |

   default: 1

   type: Unsigned Integer                                    |
   | Description |

   description: The version of DocType "DocType" interpreter used to create   |
   |             | the EBML Document.                                  |
   +-------------+-----------------------------------------------------+

   +-------------+-----------------------------------------------------+
   | Name        |
   "EBML Document".

11.2.8.  DocTypeReadVersion                                  |
   +-------------+-----------------------------------------------------+
   | Level       | 1                                                   |
   | EBML ID     | [42][85]                                            |
   | Mandatory   | Yes                                                 |
   | Multiple    | No                                                  |
   | Range       | -                                                   |
   | Default     | Element

   name: DocTypeReadVersion

   path: "1*1(\EBML\DocTypeReadVersion)"

   id "0x4285"

   minOccurs: 1                                                   |
   | Type        |

   maxOccurs: 1

   default: 1

   type: Unsigned Integer                                    |
   | Description |

   description: The minimum DocType "DocType" version an interpreter "EBML Reader" has to   |
   |             |
   support to read this EBML Document.                 |
   +-------------+-----------------------------------------------------+

1.11.3. "EBML Document".  The value of the
   "DocTypeReadVersion Element" MUST be less than or equal to the value
   of the "DocTypeVersion Element".

11.3.  Global elements (used everywhere in the format)
   +-------------+-----------------------------------------------------+
   | Name        |

   name: CRC-32                                              |
   +-------------+-----------------------------------------------------+
   | Level       | 1+                                                  |
   | Global      | Yes                                                 |
   | EBML ID     | [BF]                                                |
   | Mandatory   | No                                                  |
   | Range       | -                                                   |
   | Default     | -                                                   |
   | Type        |

   path: "*1((1*\)\CRC-32)"
   id: "0xBF"

   minOccurs: 0

   maxOccurs: 1

   size: 4

   type: Binary                                              |
   | Description |

   description: The CRC-32 Element "CRC-32 Element" contains a 32 bit 32-bit Cyclic         |
   |             | Redundancy
   Check value of all the Element Data "Element Data" of   |
   |             | the Parent Element "Parent Element" as
   stored except for the CRC-32  |
   |             | Element "CRC-32 Element" itself.  When the CRC-32 Element "CRC-32
   Element" is present, |
   |             | the CRC-32 Element "CRC-32 Element" MUST be the first ordered        |
   |             | Element
   "EBML Element" within its Parent Element "Parent Element" for easier        |
   |             | reading.  All Top-Level Elements
   "Top-Level Elements" of an EBML Document |
   |             | "EBML Document" SHOULD include a CRC-32 Element "CRC-32
   Element" as a Child Element. |
   |             | "Child Element".  The CRC in use is the IEEE-CRC-32
   algorithm as used |
   |             | in the ISO 3309 [ISO.3309.1979] standard and in section
   8.1.1.6.2   |
   |             | of ITU-T recommendation V.42, [ITU.V42.1994], with initial value of |
   |             | 0xFFFFFFFF. "0xFFFFFFFF".  The
   CRC value MUST be computed on a     |
   |             | little endian bitstream and MUST use
   little endian  |
   |             | storage.                                            |
   +-------------+-----------------------------------------------------+

   +-------------+-----------------------------------------------------+
   | Name        |

11.3.1.  Void                                                |
   +-------------+-----------------------------------------------------+
   | Level       | 0+                                                  |
   | Global      | Yes                                                 |
   | EBML ID     | [EC]                                                |
   | Mandatory   | No                                                  |
   | Multiple    | Yes                                                 |
   | Range       | -                                                   |
   | Default     | -                                                   |
   | Type        | Element

   name: Void

   path: "*((*\)\Void)"

   id: "0xEC"

   minOccurs: 0

   maxOccurs: unbounded

   type: Binary                                              |
   | Description |

   description: Used to void damaged data, to avoid unexpected      |
   |             | behaviors
   when using damaged data.  The content is   |
   |             | discarded.  Also used to
   reserve space in a sub-     |
   |             | element sub-element for later use.                              |
   +-------------+-----------------------------------------------------+

2.

12.  References

12.1.  Normative References

   [IEEE.754.1985]
              Institute of Electrical and Electronics Engineers,
              "Standard for Binary Floating-Point Arithmetic",
              IEEE Standard 754, August 1985.

   [ISO.3309.1979]
              International Organization for Standardization, "Data
              communication - High-level data link control procedures -
              Frame structure", ISO Standard 3309, 1979.

   [ISO.9899.2011]
              International Organization for Standardization,
              "Programming languages - C", ISO Standard 9899, 2011.

   [ITU.V42.1994]
              International Telecommunications Union, "Error-correcting
              Procedures for DCEs Using Asynchronous-to-Synchronous
              Conversion", ITU-T Recommendation V.42, 1994.

   [RFC0020]  Cerf, V., "ASCII format for network interchange", STD 80,
              RFC 20, DOI 10.17487/RFC0020, October 1969,
              <http://www.rfc-editor.org/info/rfc20>.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2279]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", RFC 2279, DOI 10.17487/RFC2279, January 1998,
              <http://www.rfc-editor.org/info/rfc2279>.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
              <http://www.rfc-editor.org/info/rfc3339>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <http://www.rfc-editor.org/info/rfc5234>.

   [RFC5646]  Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying
              Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646,
              September 2009, <http://www.rfc-editor.org/info/rfc5646>.

   [RFC7405]  Kyzivat, P., "Case-Sensitive String Support in ABNF",
              RFC 7405, DOI 10.17487/RFC7405, December 2014,
              <http://www.rfc-editor.org/info/rfc7405>.

   [W3C.REC-xml-20081126]
              Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and
              F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth
              Edition)", World Wide Web Consortium Recommendation REC-
              xml-20081126, November 2008,
              <http://www.w3.org/TR/2008/REC-xml-20081126>.

12.2.  Informative References
2.1.  URIs

   [1] https://tools.ietf.org/html/rfc2119

   [2] http://www.faqs.org/rfcs/rfc2279.html

   [3] http://www.w3.org/XML/Schema#dev

   [4] http://www.w3.org/TR/xml/

   [5] http://www.w3.org/TR/1999/REC-xml-names-19990114/#ns-decl

   [6] https://www.w3.org/TR/xmlschema-0/#ref6

   [7] https://www.w3.org/TR/xmlschema-0/#ref6

   [8] http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1570.pdf

   [W3C.REC-xmlschema-0-20010502]
              Fallside, D., "XML Schema Part 0: Primer", World Wide Web
              Consortium Recommendation REC-xmlschema-0-20010502, May
              2001,
              <http://www.w3.org/TR/2001/REC-xmlschema-0-20010502>.

Authors' Addresses

   Steve Lhomme

   Dave Rice

   Moritz Bunkus