Here are the crucial concepts for this chapter:
XPath expressions can be evaluated to create a result.
Location steps indicate a single step in a location path .
Location paths are used to locate data and return node-sets .
Axes let you specify how you want a location step to locate data.
Predicates are optional parts of location steps that let you be more specific about the data you want.
Nodes are the fundamental building blocks of XML documents.
Root nodes are the topmost nodes in documents.
A context node is the current node that is being processed .