Add Option to Format in often used match expression parts

[Hendiadyoin1]

Languages often have patterns that reappear in multiple places, like identifiers or argument-lists.
These can have quite some length to it and may make the match-expression as a whole less readable.

To solve this you could add a top-level dict to the grammar description that contains name-regex pairs which are substituted into the requested places at runtime.

A good solution would be to add all defined helper functions as a preamble to each match in a named group with 0 repetitions like (?<Name>...){0}

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Another possible solution might be PCRE's (?&name) (and (?(DEFINE)...)) syntax
this could be emulated via preprocessing of the patterns and string superstition,
this would not break any old code because (?&...) is illegal in ECMA's regex subset

If a switch to PCRE happens or native support is added you would just need to add a list of (?(DEFINE)...)s to the start of each match

[RedCMD]

Probably should request this at https://github.com/textmate/textmate