bug#62029: 29.0.60; Allow users to customize eldoc buffer separator

[Yuan Fu]

>> 
>> Looks good to me (except for the “documentatiok” ;-) eldoc-box can also 
>> benefit from this (right now if you use it in emacs-lisp-mode, it just shows 
>> a thin strip of text, not very exciting).
>> 
>> I’ll experiment with the title thing in eldoc-box. Does eglot and flymake 
>> already pass a :source cookie? Those two displaying stuff together is the 
>> most possible case I can think of.
> 
> 
>> it just shows a thin strip of text, not very exciting).
> 
> Indeed.  I'll present my patch soon in emacs-devel.
> There's one thing I don't like about it which is that
> is re-does a lot of complicated parsing for both *Help*
> and *eldoc* forms.  Could be slow, or could be meaningless.
> Another aspect is that function documentation looks great
> because there is this nifty describe-function-1 helper, but
> variable documentation looks poor because there is
> no such thing.

Cool! The whole help system would benefit from some renovation, but I don’t 
think anyone is excited to do it ;-)

> 
>> Does eglot and flymake already pass a :source cookie?
> 
> You mean ':origin', not ':source'.  Though the latter name is
> acceptable and there's plently of time to change to it if you
> think it's better or more consistent with other parts of Emacs.
> 
> Yes they do.  This cookie is automatic.  Maybe I should state that
> in the documentatiok.

Yeah, I think it’ll be good to mentioned them in the documentatiok.

> 
>> Those two displaying stuff together is the most possible case
>> I can think of.
> 
> In Eglot it's very usual to have three sources, and in Emacs
> Lisp you can also have three (function, variable and flymake).
> 
> You do need to set eldoc-documentation-strategy to
> eldoc-documentation-compose though (this should really
> be the default).

Huh, I wonder why I can see both flymake + eglot in the eldoc doc buffer when 
my eldoc-documentation-strategy is the default value?

Yuan