I'm looking for something more general. What I'm looking for exists in emacs, see below, where it'll give you a way of figuring out what exactly the mouse cursor is hovering over (after transforming the resulting "frame" [ie window] coordinates to "buffer" and "buffer position" and then peeking there).
That doesn't exist in sublime yet I gather?
mouse-position is a built-in function in `C source code'.
Return a list (FRAME X . Y) giving the current mouse frame and position.
The position is given in character cells, where (0, 0) is the
upper-left corner of the frame, X is the horizontal offset, and Y is
the vertical offset.