normalize expression

normalize evaluates given expression to a node-list and puts all text nodes in the full depth of the sub-tree underneath each node in the node-list into a "normal" form where only structure (e.g., elements, comments, processing instructions, CDATA sections, and entity references) separates text nodes, i.e., there are neither adjacent text nodes nor empty text nodes.

Note, that most XSH2 commands automatically join adjacent text nodes.