CSS basic box model

CSS 3 - overflow-x, overflow-y - Working Draft
CSS 2.1 - Overflow: the 'overflow' property - Candidate Recommendation
Opera 9.2x では CSS 2.1 の overflow はサポートするが、9.50 では CSS 3 の overflow-x/y もサポートする。
[20th/Jan 追記]

Some site compatibility issues can be solved by adding new functionality. That's why Kestrel includes support for things like the "overflow-x" and "overflow-y" CSS properties, JavaScript Getters and Setters, and line-/block-breaking in rich text editors. We've also fixed problems seen at Google's sites, in the default WordPress template, and in various JavaScript libraries.