
This function returns the result of applying the XPath
expression to the context node.  By default only the first result is
returned, but supplying a third argument allows you to specify an
index for the value; the default assumes a value of 1 here.  A value
of 0 returns an array of 0 or more elements, one for each value
selected by the XPath expression.
	
When this function returns an entity in a result set, the client will
see an nvarchar value containing the serialization of the entity,
complete with markup.  When the entity is passed as an SQL value it
remains an entity referencing the node of a parsed XML tree,
permitting navigation inside the tree.
	