I want to write the canonical answer to this question because the answer above has a problem.
Our problem
The CSS selector:
.foo
will select any element that has the class foo.
How do you do this in XPath?
Although XPath is more powerful than CSS, XPath doesn’t have a native equivalent of a CSS class selector. However, there is a solution.
The right way to do it
The equivalent selector in XPath is:
//*[contains(concat(" ", normalize-space(@class), " "), " foo ")]
The function normalize-space strips leading and trailing whitespace (and also replaces sequences of whitespace characters by a single space).
(In a more general sense) this is also the equivalent of the CSS selector:
*[class~="foo"]
which will match any element whose class attribute value is a list of whitespace-separated values, one of which is exactly equal to foo.
A couple of obvious, but wrong ways to do it
The XPath selector:
//*[@class="foo"]
doesn’t work! because it won’t match an element that has more than one class, for example
<div class="foo bar">
It also won’t match if there is any extra whitespace around the class name:
<div class=" foo ">
The ‘improved’ XPath selector
//*[contains(@class, "foo")]
doesn’t work either! because it wrongly matches elements with the class foobar, for example
<div class="foobar">
Credit goes to this fella, who was the earliest published solution to this problem that I found on the web:
http://dubinko.info/blog/2007/10/01/simple-parsing-of-space-seprated-attributes-in-xpathxslt/