That's a good idea. Another use case occurred to me after I wrote my comment: to ignore keywords in comments. Sometimes that can be desirable.

I keep going back lately to Rob Pike's idea that breaking files into lines is not the best approach (http://news.ycombinator.com/item?id=4111667). In that paper he proposes a regular expression for breaking up lines into structured content. But maybe there's another way. Like an ometa grammar? (http://tinlizzie.org/ometa)

Anyways, just a few random thoughts.