This question is geared towards testing via Selenium / Web Driver, though applies to general web application/development.
XPath has a very nice feature of grouping a given XPath and combining with indexing to say "give me element N for all/multiple elements returned from given XPath, specified as "(//someXpath)[n]" w/o the quotes.
I was wondering if there is a translatable equivalent in CSS. If not via standard CSS, then how about Sizzle/jQuery? If none exist, would be nice if that kind of thing be added as a CSS standard in the future. Something like a "(someCssSelector):nth-of-type(n)"
Other than that, the alternative for XPath and CSS is to be more specific in describing the DOM tree, going up the tree to get uniqueness in identifying elements (as opposed to (someShorterSimplerXpath)[n]).