You can also select attributes by adding the step: @name

For example, given the content:

<contents>
<para><a href="one.html">One</a></para>
<para><a href="two.html">Two</a></para>
<para><a href="three.html">Three</a></para>
</contents>

the expression:

/content/para/a/@href

would return the attribute 'href' of each of the three paragraphs as set.