XPath is a defines a syntax and specification for addressing
different parts of an XML document. It can also be used to address
functions in a library.
An XPath expression, when evaluated, results in a set of nodes, a
boolean, a number, or a string. XPath expressions are evaluated in a
context, which in most cases will be some node (the context node), but
which can also be a namespace, a function library, a set of variable
bindings, or a pair of non-zero integers (context position and
size).
The context is usually determined by the system doing the
processing; a XSLT processor for instance.
The nodes in this metanode will sometimes refer to this document fragment to provide some
examples:
<zoo>
<animals>
<dog breed="collie">
<cat breed="tabby">
</animals>
<people>
<person name="John" job="keeper">
<person name="Amy" job="vet">
</people>
</zoo>
Nodes:
Most of this information is condensed from the XPath specs at http://www.w3c.com/TR/XPath and from articles on http://www.xml.com/.