bug#43609: 28.0.50; eldoc-documentation-function [vs new eldoc-display-functions]

[martin rudalics]

> Anyway, this is only relevant if you're thinking of integrating
> your tooltip display in Emacs proper, eldoc or thereabouts.
> Are you?

I have to use it in practice before I can tell whether it works.  Back
then, it took me some time to make the code do what I meant - put the
tooltip in the right place of the window, move away the mouse cursor if
necessary ...

Meanwhile, please provide the compatibility layer you earlier promised
with

  But if you really insist , it's a very easy function to bring back I
  would say (in fact the function I gave you earlier is probably more
  useful generalization of it).

so we can close this bug.

Ideally, this would render your earlier changes backward-compatible and
make the obsoletion declaration for 'eldoc-documentation-function' clean
and follow our usual practice.

The downside of this approach is obviously that we would have to keep
the old definitions of 'elisp-eldoc-documentation-function' and its
colleagues around for a while.  So if you think that removing these old
definitions immediately is crucial for future development, please
provide some substitute function and mention it in the doc-string of
'eldoc-documentation-function(s)'.

Thanks in advance, martin