Feature request: support ABNF grammar in productionlist

[jsamr]

Feature

Provide support for Augmented Backus Naur Form [rfc5234] syntax in production list. The grammar option could have the following values:

• abnf-5234 for rfc5234
• abnf, alias for abnf-5234
• abnf-4234 for rfc4234
• ebnf for ISO-14977 (when supported)
• sphinx (default)

Sample

.. productionlist::
  :grammar: abnf-5234

  UPPERCASE-ALPHA = %x41-5A ; A-Z
  LOWERCASE-ALPHA = %x61-7A ; a-z

[tk0miya]

+0; I can accept it if anyone makes a PR for it.

[jashank]

I've recently run into a need for this, and am presently attempting to cobble something together.

[encukou]

For the CPython docs we now use a custom directive that formats production lists almost as-is (it only looks for strings in quotes, colons after rule names, and token references in backticks).
That might be a way to get more kinds of grammars supported.