One of the key specifications being used in XML technologies is XPath. This is a little language used within other languages for selecting nodes within an XML document (just as regular expressions is a language of its own within Perl). The initial appearance of an XPath is similar to that of a Unix directory path. In Example E-2 we can see the XPath /dromedaries/species, which starts at the root of the document, finds the dromedaries root element, then finds the species children of the dromedaries element. Note that unlike Unix directory paths, XPaths can match multiple nodes; so in the case above, we select all of the species elements in the document.

Documenting all of XPath here would take up many pages. The grammar for XPath allows many constructs of a full programming language, such as functions, string literals, and Boolean expressions. What's important to know is that the syntax we are using to find nodes in our XML documents is not just something invented for AxKit!