bug#19012: 25.0.50; `help-window-select'

[Drew Adams]

> > So there is *no* behavior for `special-display-function'
> > to follow, other than its own behavior.
> 
> Let me restate what I said in clearer terms. Of course you're
> free to do whatever you want in special-display-function, but
> if it doesn't follow the behavior described by display-buffer's 
> docstring and you get undesirable behavior, then I will
> consider it as a bug in *your* code rather than in Emacs.

And you will be wrong, at least wrt what `display-buffer' has
said about its own behavior and wrt what its behavior has been.

It is not a bug, according to what `display-buffer' says
about itself, for it to delegate its behavior to
`special-display-function'.  That *is* its intended behavior
when `special-display-function' is used.

If it interferes with that delegation in some way, that is a
bug.  If `display-buffer' itself "doesn't follow the behavior
described by display-buffer's docstring" then that is a bug
in `display-buffer'.

Of course, as Mr Emacs, you are free to change the behavior
of `display-buffer', or `car', or `setq' anyway you like.