gstreamer/docs/random/caps_grammar

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Canonical caps/structure strings (those created by gst_caps_to_string()
and gst_structure_to_string()) do not have AUTO_VALUE.
Goals:
- UTF-8 clean
- SIMPLE_STRINGs should cover most simple cases that don't interfere
with other parts of the gst_caps or gst_parse grammar
- forward-parsed grammar
- quoted strings handle backslash escaping as well as XML-style (&ack;)
escaping
CAPS = STRUCTURE [ ';' STRUCTURE ]*
STRUCTURE = STRUCTURE_NAME [ ',' FIELD ]*
STRUCTURE_NAME = STRING
FIELD = FIELD_NAME '=' TYPED_VALUE
FIELD_NAME = SIMPLE_STRING
TYPED_VALUE = CANONICAL_VALUE | AUTO_VALUE
CANONICAL_VALUE = '{' TYPED_VALUE [ ',' TYPED_VALUE ]* '}'
| '[' TYPED_VALUE ',' TYPED_VALUE ']'
| '(' TYPE ')' VALUE
AUTO_VALUE = [-+]?[0-9][0-9]*
| [-+]?[0-9][0-9]*[.][0-9]*[eE][-+][0-9]*
| STRING
VALUE = STRING
STRING = ["][^"]["]
| ['][^'][']
| SIMPLE_STRING
SIMPLE_STRING = [A-Za-z0-9_+-:./]+
TYPE = "int" | "i" | "float" | "f" | "double" | "d" | "fourcc" | "4"
| "boolean" | "bool" | "b"
| GTYPE
Canonical Examples:
"audio/raw"
"audio/raw", rate=(int)44100
"audio/raw", rate=(int)44100, signed=(boolean)true
"audio/raw", rate={ (int)44100, (int)48000 }
"audio/raw", rate=[ (int)8000, (int)48000 ]