[css3-transitions] What is allowed for 'transition-property'?

The definition of 'transition-property' at
http://dev.w3.org/csswg/css3-transitions/#the-transition-property-property-
(what's with the "-" at the end of all the section IDs in this spec?)
doesn't say what values are legal and what values are not.  In
particular:

 (1) is it a syntax error if an unknown property is in the list?
 (2) is it a syntax error if a shorthand property is in the list?
 (3) is it a syntax error if a non-animatable property is in the list?
 (4) is it a syntax error if 'none', 'all', 'inherit', or 'initial'
     occurs within the list?

(In summary, my suggestions are 1-3 no, and 4 yes.)


For (1), I think it's a bad idea to make unknown properties parse
errors, because then if authors want to use new properties in
transitions, they'd have to declare the transition-property property
many times over.

For (2), I think it's also bad to make shorthands an error, since
the group has taken the strategy of making longhands into
shorthands.  I think shorthands should be animatable, which would
mean that any subproperty of the shorthand that is animatable
animates according to the corresponding function/duration/delay.

For (3), I think it's also bad, because we may decide to expand the
list of properties that are animatable over time, so it poses the
same problem as (1).

For (4), I don't have strong opinions, except I don't see any reason
to differ from the 'counter-increment' and 'counter-reset'
properties.  I think the behavior should be defined.

-David

-- 
L. David Baron                                 http://dbaron.org/
Mozilla Corporation                       http://www.mozilla.com/