Sizzle Selector Engine Question:

Sizzle supports virtually all CSS 3 Selectors - this even includes some parts that are infrequently implemented such as escaped selectors (".foo\+bar"), Unicode selectors, and results returned in document order. There are a few exceptions to CSS3 selector support. These exceptions are only limited to selectors that would require events added to the DOM to keep track of the state of elements. For instance, the following pseudo-selectors are not supported:

:hover
:active
:visited
:link (this is the opposite of :visited and also requires an event)

Note: Some CSS3 selectors were not supported until version 1.9. These were added in 1.9:

:target
:root
:nth-last-child
:nth-of-type / :nth-last-of-type / :first-of-type / :last-of-type / :only-of-type
:lang()