Expressions in XPath include the sorts of structures, operators, and data types found in most computer languages, albeit with a few differences. This section gives an overview of these distinguishing features. Consult the XPath Recommendation [XPath] for the full details. Note that location paths can appear in expressions, and expressions can appear in location paths as predicates (see Section 6.3.4).
|//||Equivalent to the location step
Because this path is defined as ending with a slash, it cannot occur at the end of a location path. Because it is defined as starting with a slash, when it occurs at the beginning of a location path, that ...