allout-widgets-tally-string is a compiled Lisp function in `
Return a string giving the number of tracked widgets, or empty string if not tracking.
The string is formed for appending to the allout-mode mode-line lighter.
An empty string is also returned if tracking is inhibited or
widgets are locally inhibited.
The number varies according to the evanescence of objects on a
hash table with weak keys, so tracking of widget erasures is often delayed.