A location path selects a set of nodes from an XML document.
Each location path is composed of one or more location steps.
Each location step has an axis, a node test and may have one or more predicates.
Each location step is evaluated with respect to a particular context node.
A double colon (::) separates the axis from the node test.
Each predicate is enclosed in square brackets.
Examples:
child::PERIODIC_TABLE
descendant::ATOM[1]
ancestor::ATOM
following-sibling::ATOM[ATOMIC_NUMBER="3"]
descendant-or-self::ATOM[]
child::*
descendant-or-self::node()
attribute::UNITS