Re: etc/TODO:Horizontal scrollbar

[Richard Stallman]

    and did other changes for horizontal scroll. I am facing problems in
    "redeem"... I need to understand the way windows in GNU Emacs works
    before I can come up with a robust solution.

It is a sort of GC for scroll bars.  Redisplay marks all scroll
bars as possibly to be freed, then when it redisplays a window,
it marks that window's scroll bar as "still in use".  I think
that redeem_scroll_bar does the latter part of the job.
At the end,. those that weren't redeemed are really deallocated.