Today you learned that elements and attributes alike are referred to as nodes. You also learned that a node with child nodes (elements) is called a tree fragment. Using XPath expressions, you can also match nodes in different parts of an XML document. If the match expression matches more than one node, the result is a node-set in which each node can be referred to by number within the node-set. A node-set is not a hierarchy of nodes.
You select nodes by using XPath expressions. They consist of location paths, which in turn consist of an axis, a node test, and a predicate. The axis and predicate are optional. If no axis is specified, it is implied. If no predicate is specified, all nodes that match the axis and node test will match.
Tomorrow you will learn more information about templates. You will use many of the rules you learned today about XPath expressions as you learn more about templates and controlling the flow of control.