php - Selecting a css class with xpath

Question

I want to select just a class on its own called .date

For some reason, I cannot get this to work. If anyone knows what is wrong with my code, it would be much appreciated.

@$doc = new DOMDocument();
@$doc->loadHTML($html);
$xml = simplexml_import_dom($doc); // just to make xpath more simple
$images = $xml->xpath('//[@class="date"]');                             
foreach ($images as $img)
{
    echo  $img." ";
}

Answer 1

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/