W3C home > Mailing lists > Public > www-style@w3.org > September 2010

[css-mobile] behaviour of shorthands only partly in css-mobile

From: Peter Moulder <peter.moulder@monash.edu>
Date: Fri, 03 Sep 2010 14:22:18 +1000
To: www-style@w3.org
Message-id: <20100903042218.GA4218@bowman.infotech.monash.edu.au>
A number of the properties listed at http://www.w3.org/TR/css-mobile/
are shorthand properties where some of the "component" properties
are either not part of css-mobile at all, or support only a strict subset of
the values that CSS2.1 supports for that property.

Take the 'font' property, for example, which in CSS2.1 allows specifying a
number of properties including 'font-size' and 'line-height'.  css-mobile says
that 'font' is supported and has the same syntax as in CSS2.1, but that
'line-height' is not part of css-mobile, and that 'font-size' is supported but
with a limited set of values, such as not allowing <length> values.

This leads to some doubt as to what a css-mobile user agent should do with

  font: bold 14px/17px Times

or variations on that: whether the whole declaration should be dropped,
or whether it should first be expanded to font-weight:bold etc. and then
dropping those components that the user agent doesn't support.

The css-mobile document tries to provide an answer to this question by

  Limitations that apply to a property apply equally to its shorthand

but for me that actually makes things less clear, because it's ambiguous
as to whether it means "limitations in effect" (dropping just the 'font-size'
and 'line-height' components in the above example) or "limitations in what is
considered a valid value for the shorthand property" (dropping the whole

If the answer to the above is that the whole shorthand declaration should be
dropped, then:

  Another possible issue is the question of what's meant by "limitations that
  apply to a property" in the case that the property isn't part of css-mobile:
  the most natural answer to the question "what are the limitations applicable
  to list-style-position" would be "it's constrained to its initial value (viz.
  'outside')", in which case

    list-style: square outside

  is a valid declaration, whereas a more liberal interpretation would be
  be that the valid syntax for 'list-style' changes from

    [ <'list-style-type'> || <'list-style-position'> || <'list-style-image'> ] | inherit


    [ <'list-style-type'> || <'list-style-image'> ] | inherit

  The corresponding change for 'font' would presumably drop not just
  <'line-height'> but the whole [ / <'line-height'> ]? portion of the syntax.

  If this more liberal interpretation is in fact the intention, then I'd be
  inclined to give the revised syntax explicitly, and to add a note that e.g.
  <'font-size'> refers to the set of values in css-mobile rather than in

Received on Friday, 3 September 2010 04:22:50 UTC

This archive was generated by hypermail 2.3.1 : Wednesday, 11 February 2015 12:34:41 UTC