The required select attribute contains an expression. When the result of evaluating the expression is a result tree fragment,
the complete fragment is copied into the result tree. When the result is a node-set, all the nodes in the set are copied in
document order into the result tree; copying an element node copies the attribute nodes, namespace nodes and children of the
element node as well as the element node itself; a root node is copied by copying its children. When the result is neither
a node-set nor a result tree fragment, the result is converted to a string and then inserted into the result tree, as with
xsl:value-of.
Examples (xslt:xml): Overview 30:7