Python XML processing with lxml

See Section 16.5, “rnck: fatal()”.

# - - -   u s a g e

def usage(*L) :
    '''Write an error message and terminate.

      [ L is a list of strings ->
          sys.stderr  +:=  (concatenation of elements of L)
          stop execution ]
    '''
    fatal("*** Usage:\n"
            "***   %s SCHEMA FILE ...\n"
            "*** %s" %
            (sys.argv[0], ''.join(L)))
    raise SystemExit