RE: [Feature request] face property `raise'

["Wedler, Christoph" <christoph.wedler@sap.com>]

rms@gnu.org writes:

 > It sounds like the main reason you would rather use a face
 > is so that you could specify a symbol and define the symbol's
 > meaning elsewhere.  Currently that can be done for the face
 > property but not for the display property.

 > Is that ability to refer to a symbol whose meaning is
 > defined elsewhere the real issue?

Exactly.  (And we have this symbol already: the symbol naming a face.)

What we like to have in Emacs is:

 1. the ability to assign various properties (let's use the simple name
    for the moment) to text (parts)

 2. the ability to define "abstract" properties and assign one ore more
    of them to text (parts).  Each abstract property represents a list of
    (concrete) properties (with their values).

If you read this you might think that the properties which can be
assigned directly via 1 and those which can be assigned indirectly via 2
should be basically the same.

I would agree.  And this is how things work in HTML/CSS.

In fact, there is already a property which can be assigned via 1 and 2
in Emacs:

 1. the font-size can be assigned via the display property `height'

 2. the font-size can be assigned via the font of a face

    (Emacs new font selection mechanism is already an important step in
    the right direction: the font is not a useful property, the
    font-size, font-family, etc are useful properties, a font is just
    used for the physical representation of a couple of properties.)

Some properties might not be useful to assign indirectly => you provide
them as display properties only.

Some or indeed all properties which are currently just face properties
are probably also useful for direct assignment => you could make them
display properties, too (e.g., color, etc).

In conclusion: Emacs already has abstraction mechanism, it is just
called a bit strangely (face) and presented as standing beside the
display properties.

- Christoph