Opera Developer News

The CSS specification allows for vendor-specific extensions. These are usually (but not exclusively) used for experimental additions to the CSS specification that have not yet reached Candidate Recommendation stage. The following are used in Opera 10.5x and Opera 10.60:

• -o-table-baseline see A MathML for CSS Profile
• -o-text-overflow see CSS3 Text Module section
• -o-transform see CSS 2D Transforms Module Level 3
• -o-transform-origin see Transforms Module Level 3
• -o-transition see CSS Transitions Module Level 3 (Partial support, see http://www.opera.com/docs/specs/presto25/css/transitions/). CSS transitions are supported on certain animatable properties.
• -o-transition-delay see CSS Transitions Module Level 3
• -o-transition-duration see CSS Transitions Module Level 3
• -o-transition-property see CSS Transitions Module Level 3
• -o-transition-timing-function see CSS Transitions Module Level 3

In addition to using -moz-, -ms-, -o- and -webkit- extensions (I usually put them in alphabetical order), the final declaration should use the unprefixed version. That way, future browsers that include the feature after it becomes fully standardised can apply the style.

(This carries a risk that the specification might change, but if you choose to use experimental features on production sites you need to be aware that there is a risk. The risk a spec may change is a better bet than the certainty that future browsers won't be able to use your rules if you don't use a non-prefixed version: see Bruce's Writing cross-browser, future-proof CSS 3 for more discussion.)

Opera 10.5x also supports the extension -o-tab-size which defines how many spaces a tab character displays as inside <pre>, for example {-o-tab-size:3;}.

We also publish a full list of Web specifications supported in Opera Presto 2.5.

Peter Beverloo has written an Overview and comparison of vendor-prefixed CSS properties.