Notes

thingatpt.el

Emacs's thingatpt.el provides an API for defining text objects known as 'things', and querying the buffer for them. I want to add my own 'things' but the documentation isn't that clear (they say to do one thing, but do another internally). However, after reading most of the functions thingatpt.el defines, things become a lot clearer. In short, there are a few requirements to define a 'thing':

1. You must define 'forward-op to use forward-thing. This is the only operation you have to define since all other operations can be emulated with just forward-thing. So for the rest of the operations we will talk about, it is assumed 'forward-op is either nil or are more efficient implementation exists.

   (put 'wordv2 'forward-op
     (lambda (&optional count)
       (interactive "p^")
       (setq count (or count 1))
       (forward-word count)))
   

2. You may define both 'beginning-op and 'end-op, or just 'bounds-of-thing-at-point to use bounds-of-thing-at-point. If 'forward-op is not defined, you must define either one to use bounds-of-thing-at-point.

   (put 'bufferv2 'end-op
     (lambda () (goto-char (point-max))))
   (put 'bufferv2 'beginning-op
     (lambda () (goto-char (point-min))))
   
   (put 'bufferv2 'bounds-of-thing-at-point
     (lambda () (cons (point-min) (point-max))))
   

3. You may define 'thing-at-point directly to use thing-at-point.

   (put 'filenamev2 'thing-at-point
     (lambda (&optional _lax _bounds)
        (when-let ((filename (thing-at-point 'filename)))
          (setq filename (expand-file-name filename))
          (and (file-exists-p filename) filename))))