You are looking for the descendant axis:
the
descendantaxis contains the descendants of the context node; a descendant is a child or a child of a child and so on; thus the descendant axis never contains attribute or namespace nodes
In your case: /descendant:t
Of course, as others have answered, there is an abbreviated syntax for this:
//is short for/descendant-or-self::node()/. For example,//parais short for/descendant-or-self::node()/child::paraand so will select anyparaelement in the document (even aparaelement that is a document element will be selected by//parasince the document element node is a child of the root node)