I asked this in another thread, and was pointed to a partial answer, but will give it another go more clearly.

Is there anywhere (webpage, wiki page, source code) that clearly lists the available scopes that are treated as the assumptive default basis? There is the old page at: http://manual.macromates.com/en/scope_selectors but it appears to be out of date, and it doesn't describe the new events (triggers?) such as callback.*

In addition, I know that bundles can define their own such selectors, which brings me to my next question/request:

Is it possible to have TM2 report the currently available scopes? We have the ability to report the stack of scopes under the current cursor/selection(Ctrl-Shit-Cmd-P), but I'd like to see all the available scopes registered. (Perhaps limit it to the current document type/active language bundle.)

Right now I have many bundle ideas, but no idea what is possible to work with, what would need to be extended in TM2 itself, etc. Knowing the lay of the land would go a long ways towards forming a mental model of how to approach various tasks.