XML in a Nutshell, 3rd Edition

Location Paths

Node- sets are returned by location-path expressions. Location paths consist of location steps. Each location step contains an axis and a node test separated by a double colon. That is, a location step looks like this:

               axis::node test

The axis specifies in which direction from the context node the processor searches for nodes. The node test specifies which nodes along that axis are selected. These are some location steps with different axes and node tests:

child::set
descendant-or-self::node( )
ancestor-or-self::*
attribute::xlink:href

Each location step may be suffixed with predicates enclosed in square brackets that further winnow the node-set. For example:

child::set[position( )=2]
descendant-or-self::node( )[.='Eunice']
ancestor-or-self::*[position( )=2][.="Celeste"]
attribute::xlink:href[starts-with(., 'http')]

Each individual location step is itself a relative location path. The context node against which the relative location path is evaluated is established by some means external to XPath—for example, by the current matched node in an XSLT template.

Location steps can be combined by separating them with forward slashes. Each step in the resulting location path sets the context node (or nodes) for the next path in the step. For example:

ancestor-or-self::*/child::*[position( )=1]
child::document/child::set[position( )=2]/following-sibling::*
descendant::node( )[.='Eunice']/attribute::ID

An absolute location path is formed by prefixing a forward slash to a relative ...