css3-conditional/Overview.src.html

changeset 6741
ce28a0e42de9
parent 6740
37b94dbfec45
child 6742
911a391cb16c
     1.1 --- a/css3-conditional/Overview.src.html	Thu Sep 20 12:43:23 2012 -0700
     1.2 +++ b/css3-conditional/Overview.src.html	Thu Sep 20 13:03:53 2012 -0700
     1.3 @@ -564,26 +564,28 @@
     1.4  
     1.5  <h3 id="support-definition">Definition of support</h3>
     1.6  
     1.7 +<p>For forward-compatibility,
     1.8 +<a href="http://www.w3.org/TR/CSS21/syndata.html#declaration">section 4.1.8
     1.9 +(Declarations and properties)</a> of [[!CSS21]]
    1.10 +defines rules for handling invalid properties and values.
    1.11 +CSS processors that
    1.12 +do not implement or partially implement a specification
    1.13 +<strong>must</strong> treat any part of a value that they
    1.14 +do not implement, or
    1.15 +do not have a usable level of support for,
    1.16 +as invalid according to this rule
    1.17 +for handling invalid properties and values,
    1.18 +and therefore <strong>must</strong> discard the declaration as a parse error.</p>
    1.19 +
    1.20  <p>A CSS processor is considered to <dfn id="dfn-support">support</dfn>
    1.21 -a declaration (consisting of a property and value) if it implements the
    1.22 -given value of the given property.</p>
    1.23 +a declaration (consisting of a property and value) if it accepts that
    1.24 +declaration (rather than discarding it as a parse error).
    1.25 +If a processor does not implement, with a usable level of support,
    1.26 +the value given,
    1.27 +then it <strong>must not</strong>
    1.28 +accept the declaration or claim support for it.</p>
    1.29  
    1.30 -<h3 id="partial-implementations">Partial implementations</h3>
    1.31 -
    1.32 -<p>For forward-compatibility, <a
    1.33 -href="http://www.w3.org/TR/CSS21/syndata.html#declaration">section 4.1.8
    1.34 -(Declarations and properties)</a> of [[!CSS21]] defines rules for
    1.35 -handling invalid properties and values.  CSS processors that partially
    1.36 -implement a specification <strong>must</strong> treat any part of a
    1.37 -value that they:</p>
    1.38 -<ul>
    1.39 -  <li>do not implement, or</li>
    1.40 -  <li>do not have a usable level of support for,</li>
    1.41 -</ul>
    1.42 -<p>as invalid according to this rule
    1.43 -for handling invalid properties and values,
    1.44 -and <strong>must not</strong>
    1.45 -accept or support a declaration containing such a value.  This allows
    1.46 +<p>This equivalence between declaration acceptance and ''@supports'' allows
    1.47  authors to use fallback (either in the [[CSS1]] sense of declarations
    1.48  that are overridden by later declarations or with the new capabilities
    1.49  provided by the ''@supports'' rule in this specification) that works

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