Customization of Editor -- Add a Language and/or Extension?

I've tried adding an extension in the "File Extensions" at the bottom of the preferences page for the editor but see no effect--it doesn't show that extension in a FileOpen selection list for file types so what's the purpose?

Also, there seems to be no way to add a language to the syntax highlighting list although surely that has to be implemented through some set of language definition files/macros???

I did some searching and found some info on Yair's site regarding extending some functionality with callbacks, but nothing regarding these areas.

Is the former a bug or am I missing something and if can have a listing for TLC (whatever that is?) where's Fortran?

It would be a_good_thing (tm) if the editor selection instead of being global could be language/file extension specific...then wouldn't be such an issue of having to add a specific customization.