Document fact that inherit only works when its alone.

git-svn-id: http://htmlpurifier.org/svnroot/htmlpurifier/trunk@315 48356398-32a2-884e-a903-53898d9a118a

library/HTMLPurifier/AttrDef/Multiple.php

@@ -8,6 +8,10 @@ require_once 'HTMLPurifier/AttrDef.php';
  * Certain CSS properties such as border-width and margin allow multiple
  * lengths to be specified.  This class can take a vanilla border-width
  * definition and multiply it, usually into a max of four.
+ * 
+ * @note Even though the CSS specification isn't clear about it, inherit
+ *       can only be used alone: it will never manifest as part of a multi
+ *       shorthand declaration.  Thus, this class does not allow inherit.
  */
 class HTMLPurifier_AttrDef_Multiple extends HTMLPurifier_AttrDef
 {