The doc http://code.google.com/chrome/devtools/docs/elements.html says it supports XPath or CSS selectors, but when I tried, didn't seem to work for me.
Any one knows how to use it?
Just typing xpath expression in the search box should work. It works for me in tip-of-tree build.
The feature seems to be broken in Chrome 11 though, I've filed a bug on this: http://crbug.com/79716
You can use $x in the Chrome javascript console. No extensions needed.
$x
ex: $x("//img")
$x("//img")
For xpath searches use $x('xpathSelector'). For a css selector use $('cssSelector').
$x('xpathSelector')
$('cssSelector')
However, this last selector returns only the first matching element. If you want to see all matching elements go for $$('cssSelector')
$$('cssSelector')
If you click on any element in the elements pane then type command-F, it will open a search bar that lets you search for elements using xpath selectors.