def simplify(node):

    '''Simplifies the XML functions in an XML tree.

    * Merges nodes tagged as mergable

    * Applies a pass-through optimization for aggregating functions with one arg

    '''

    for child in xml_dom.NodeElemIter(node): simplify(child)

    merge_tagged(node)

    name = node.tagName

    if not is_func_name(name): return # not a function

    items = list(xml_dom.NodeElemIter(node))

    if len(items) == 1 and items[0].tagName.isdigit(): # single numeric param

        # pass-through optimization for aggregating functions with one arg

        xml_dom.replace(node, items[0].firstChild) # use first arg's value