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