[TxMt] CSS Edit like preview

I'm looking to implement a CSS Edit like "Live Preview" either as a Textmate Plugin (or something simpler if that's an option). The problem of updating an HTML document loaded from anywhere is simple Cocoa and Javascript. The part I'm struggling with is getting access to the current textmate document as an NSString (or something else workable).

I'm able to get access to OakTextView instance and OakDocument instance in the plugin, but I just can't figure out how to get a copy of the current document. xmlRepresentation is the closest I can get, but it's not really what I want. Can anyone point me in the right direction for that?