Steve,
Here is a simple little function that takes all the lines in a buffer
(starting at the point) and creates an extent around them. It also
sets the face to blue and the mouse face to highlight.
Hope this helps,
Sean
(defun extent-it ()
(interactive)
(let (extent)
(while (re-search-forward "^[a-z]+$" nil t)
(setq extent
(make-extent (match-beginning 0) (match-end 0)))
(set-extent-face extent 'blue)
(set-extent-mouse-face extent 'highlight))))