Computed Values Patterns

This page lists a number of design patterns that have been identified for computed values.

If you're a spec editor, you should check the “computed value:” definition of the properties in your spec with this document.

1. computed values should depend only on the specified or computed values of properties on the element or its parent
2. computed values must never depend on layout
3. shorthand properties do not have computed values. For them, simply specify:
   • Computed value: see individual properties
4. url() resolvability cannot affect the computed value, since the concept of computed value shouldn't require accessing the network.
5. which format a url() resource is (e.g. whether the browser supports it) also cannot affect the computed value
6. URIs in computed values are absolute. E.g.
   • Computed value: as specified, except with any relative URLs converted to absolute
7. properties that just accept keyword or IDREF values, should just specify:
   • Computed value: as specified
8. (disputed) computed values should never depend on containing block hierarchy (though note that they already do in CSS21, eg 'height' for percentage values (http://lists.w3.org/Archives/Public/www-style/2011Sep/0008.html)