Extended Notation for Representing RIFF Form Definitions

To unambiguously define the structure of new RIFF forms, document the RIFF form using the basic notation along with the following extended notation:

Notation

Description
<name>
A label that refers to some element of the file, where <name> is the name of the label. Examples follow:

<NAME-ck>
<GOBL-form>
<bitmap-bits>
<foo>

Conventionally, a label that refers to a chunk is named <ckID-ck>, where 'ckID' is the chunk ID. Similarly, a label that refers to a RIFF form is named <formType-form>, where "formType" is the name of the form's type.

<name>  elements
The actual data represented by <name> is defined as elements.

This states that <name> is an abbreviation for elements, where elements is a sequence of other labels and literal data. An example follows:

<GOBL-form>  RIFF ( 'GOBL' <form-data> )

This example defines label <GOBL-form> as representing a RIFF form with chunk ID 'GOBL' and data equal to <form-data>, where <form-data> is a label that would be defined in another rule. Note that a label may represent any data, not just a RIFF chunk or form.

<name:type>
This is the same as <name>, but it also defines <name> to be equivalent to <type>. This notation obviates the following rule:

<name>  <type>

This allows you to give a symbolic name to an element of a file format and to specify the element data type. An example follows:

<xyz-coordinate>  <x:INT> <y:INT> <z:INT>

This defines <xyz-coordinate> to consist of three parts concatenated together: <x>, <y>, and <z>. The definition also specifies that <x>, <y>, and <z> are integers. This notation is equivalent to the following:

<xyz-coordinate>  <x> <y> <z>
<x>  <INT>
<y>  <INT>
<z>  <INT>

[elements]
An optional sequence of labels and literal data. Surrounded by square brackets, it may be considered an element itself. An example follows:

<FOO-form>  RIFF('FOO' [<header-ck>] <data-ck>)

This example defines form "FOO" with an optional header chunk followed by a mandatory data chunk.

el1 | el2 | ... | elN
Exactly one of the listed elements must be present. An example follows:

<hdr-ck>  hdr(<hdr-x> | <hdr-y> | <hdr-z>)

This example defines the 'hdr' chunk's data as containing one of <hdr-x>, <hdr-y>, or <hdr-z>.

element...
One or more occurrences of element may be present. An ellipsis has this meaning only if it follows an element; in cases such as "el1|el2|...|elN," the ellipsis has its ordinary English meaning. If there is any possibility of confusion, an ellipsis should only be used to indicate one or more occurrences. An example follows:

<data-ck>  data(<count:INT> <item:INT>...)

This example defines the data of the 'data' chunk to contain an integer <count>, followed by one or more occurrences of the integer <item>.

[element]...
Zero or more occurrences of element may be present. An example follows.

<data-ck>  data(<count:INT> [<item:INT>]...)

This example defines the data of the 'data' chunk to contain an integer <count> followed by zero or more occurrences of an integer <item>.

{elements}
The group of elements within the braces should be considered a single element. An example follows:

<blorg>  <this> | {<that> | <other>}...

This example defines <blorg> to be either <this> or one or more occurrences of <that> or <other>, intermixed in any way. Contrast this with the following example:

<blorg>  <this> | <that> | <other>...

This example defines <blorg> to be either <this> or <that> or one or more occurrences of <other>.

struct { ...} name
A structure defined using C syntax. This can be used instead of a sequence of labels if a C header (include) file is available that defines the structure. The label used to refer to the structure should be the same as the structure's typedef name. An example follows:

<3D_POINall struct {
                   INT x;      /* X-coordinate */
                   INT y;      /* Y-coordinate */
                   INT z;      /* Z-coordinate */
               } 3D POINT

Because these types are more portable than C types such as int. The structure fields are assumed to be present in the file in the order given, with no padding or forced alignment.

Unless the RIFF chunk ID is 'RIFX', integer byte ordering is assumed to be in Intel format.

/* comment */
An explanatory comment to a rule. An example follows:

<weekend>  'Sat'|'Sun'     /* Four-character code */
                             /* for day */

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