RE: [Feature request] face property `raise'

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

Kai Grossjohann wrote:
 > "Wedler, Christoph" <christoph.wedler@sap.com> writes:

 >> >     I would like to see a face property `raise' with the same
 >> >     semantics as the display property `raise'.
 >> 
 >> > I don't think so.  Raising is not a matter of how something is
 >> > displayed, but where it is displayed.
 >> 
 >> Where something is displayed (at least relatively, and that's what
 >> `raise' is about) is a special case of how something is displayed.

 > [...] So I agree with Richard that it is about "where", and much less
 > about "how".  ({Super,sub,...}scripts are usually smaller, so that
 > the size could be added to "how".)

Hm, my point[1] was that the where-vs-how distinction is not only
unclear[2], it's also not the right distinction to decide which property
should be a display property and which a face property (the property
`image' is clearly "how" and should be made a face property if I follow
Richards reasoning).

IMHO, the right distinction is:

 1. If the value of a property is specific for ONE PART of the buffer,
    it is useful to have this property as a DISPLAY property.

 2. If the value of a property is the same for a CLASS of characters in
    the buffer, it is useful to have this property as a FACE property.

Example for 1: absolute positions (one kind of "where") are specific to
one part of the buffer and are therefore useful for a display property
(e.g., :align-to).

Example for 1: most images shouldn't be displayed more than once in a
buffer, i.e., there are specific to one part of the buffer => the image
property is correctly a display property (images don't have to do
anything with "where", don't they?  ...but clearly with "how"!).  (To
support images as icons, one could imagine `image' as a face property,
too.)

Example for 2: property `raise' (I have already provided 2-3 examples:
super-/subscripts and footnote numbers).  If you have an example where
it is useful to assign this property to one specific part of the buffer
(and want a display property for this), that fine for me, but please
make `raise' a face property, since it is mostly used for a CLASS of
characters.

- Christoph

[1] unfortunately, only the intro of my message was cited, not part of
the rest of the 45 lines...

[2] relative-"where" can be seen as a specific "how".  Kai, of course,
if R (relative-"where") is a subset of W ("where") and H ("how"), and x
(property raise) is an element of R, then x might be more about W than
H, but it remains the fact that x is also an element of H.