There's a node "Input Focus" in the ELisp manual. What is missing
from it to cover what you want?
In my scheme of Emacs-ware, there's no such thing as "redirecting
input to a window".
Input is redirected to a frame, and then the
selected window on that frame is usuallythe one that reacts to user
input (I say "usually' because some input, like mouse gestures, can
operate on n on-selected windows).
> I read through parts of the Elisp manual. The section on Windows does not explain
> how to redirect user input ot an arbitrary window. The top-level on Frames does
> not either. It is not until I get to the section on Input Focus that I get any
> helpful information on this and that section refers only to frames, not selected
> windows.
Then perhaps the only stuff that's missing is some appropriately
worded index entries that lead to "Input Focus", and maybe also short
notes with cross-references elsewhere in the manual.