Imagine the following XML:
<root>
<element foobar="hello_world" />
<element example="this is one!" />
</root>
The following XPath expression:
/root/element[@foobar = 'hello_world']
will return the <element foobar="hello_world" />
element.
double quotes can also be used:
/root/element[@foobar="hello_world"]