[TxMt] Re: Use injection scopes to disable/override existing rules

[Allan Odgaard]

On 11 Jan 2016, at 13:45, Mike McQuaid wrote:

> Another question about my GitHub Markdown bundle (which I’d like to 
> propose become official when it’s good enough).

We’ve had a bunch of requests for fenced code blocks, so it would 
certainly be nice with an “official” GitHub Flavored Markdown 
bundle.

> The underscore handling in GitHub Flavoured Markdown 
> (https://help.github.com/articles/github-flavored-markdown/#multiple-underscores-in-words) 
> basically means I need to disable/override all of the existing 
> underscore handling in the GitHub Markdown bundle. Is that possible 
> somehow?

When you inject using the `L:` prefix then your rules run before the 
root grammar’s.

So while you can’t disable the rules, you can inject your rules before 
the default rules, and then match whatever they would match, so that 
they never see it.

For the underscore handling, one solution could be to make a rule that 
matches something like this: `_(?=\w)(?<=\w_)` (this regexp will match 
underscores with word characters on both sides, but not make the word 
characters part of the actual match).

Name that match something like `meta.interword-underscore.ghf-markdown` 
and since your injected rule now “eats” the underscore, the default 
rule will not see it, and should not go into emphasis mode for this 
interword underscore.