bug#20540: 25.0.50; Document tooltip woes, including `help-echo'

[Eli Zaretskii]

> Date: Sat, 9 May 2015 16:27:05 -0700 (PDT)
> From: Drew Adams <drew.adams@oracle.com>
> 
> 1. If you create a tooltip using, say, `x-show-tip', you can control the
> font, text color and size, background color, etc.  Well, only some frame
> parameters seem to have any effect, when passed in argument PARMS.  Just
> which parameters can or cannot be used for PARMS should be documented.
> 
> 2. The word `tooltip' is hardly mentioned in the doc.  Another doc fix
> would be to document `tooltip-mode' properly in the Elisp manual, saying
> which frame parameters you can use for `tooltip-frame-parameters', etc.
> 
> 3. A related bug in `tooltip.el' is that the defcustom for
> `tooltip-frame-parameters' has no :type.  Impossible for a user to
> customize the value properly using Customize.  And no help about which
> parameters can be used effectively (see #2, above).
> 
> 4. `help-echo': No doc saying whether the string can be propertized, and
> if so, which properties have any effect.  Although `x-show-tip' seems to
> let you change the char size, color, background color, etc., and you can
> use property `display' with `help-echo', apparently you cannot change
> the face attributes of the `help-echo' string so that the appearance
> changes.  This is quite a limitation, AFAICT.
> 
> All of this kind of thing should be documented: what you can and cannot
> do - which parameters have an effect.  You can make `help-echo' show an
> image instead of text, but you cannot simply change the text appearance
> of a `help-echo' string?  How are users supposed to guess what is
> possible?  Should be documented.

You've omitted the facts you've found, for some reason.  That's a bad
idea: since no one really knows about these limitations, if you want
to raise the chances that this bug report will be acted upon, I urge
you to describe everything you tried and found not to work, so that
whoever takes upon this task will have the "bread-crumbs" to go by.

Otherwise, researching this issue from scratch is an unpleasant task
that is unlikely to find its volunteer.

Thanks.