Re: Idea: Be able to use text properties as face attributes

[Eli Zaretskii <eliz@gnu.org>]

> Date: Mon, 27 Mar 2017 13:01:34 -0700 (PDT)
> From: Drew Adams <drew.adams@oracle.com>
> Cc: emacs-devel@gnu.org
> 
> > As I explained, the display engine, which is the part that implements
> > the faces, will be unable to do anything with attributes that don't
> > affect display.
> 
> Yes, you explained that.  Thanks.
> 
> Does that mean that such code could not invoke _other_ code
> that _would_ be able to do something with those text properties
> (that masquerade in a face spec as face attributes)?

We can invoke (almost) any code we like, but the question is what
would that other code do with those attributes?  Those attributes,
like their corresponding text properties, have their effect when the
corresponding Emacs features are invoked, like buffer text
modification for the 'read-only' property or keyboard input processing
for the 'keymap' property.  There's nothing we could do with these
attributes during processing of faces by the display engine, except
record those attributes somewhere, for future use by their respective
features.  Text properties are precisely a way to record such
information, but you don't want to use text properties in this case.
So some other means of recording the information will have to be
invented.  But since those means will most probably be very similar to
text properties, at least implementation-wise, what would be the point
of inventing that?

> > And the implementation of the features which do need
> > to pay attention to such attributes is entirely unrelated to faces.
> > So I don't understand why you want this to be attributes of faces.
> 
> I think by now you should understand why I proposed the
> feature - its use.  I've made that pretty clear.
>
> You are free to think that it's a useless feature, of course,
> and you are free to think that it might be useful but is not
> feasible to implement.

Sorry, I don't understand.  My questions and my confusion are real, so
please bear with me and don't assume I'm repeatedly asking the same
questions for argument's sake.  I'm asking them because I really don't
understand your motivation for proposing this feature in the form that
you proposed it.  It's your proposal, so only you can explain its
details.