code: def add_prefix(prefix, s):
      "Add `prefix` to all unprefixed names in `s`"
      # tokenize the XPath expression
      toks = xpath_lexer.scan(s)
      # add default prefix to unprefixed names
      toks2 = [_add_prefix(prefix, tok) for tok in toks]
      # build a string of the patched expression
      ls = [x.value for x in toks2]
      return ''.join(lsf add_prefix(prefix, s):
      "Add `prefix` to all unprefixed names in `s`"
      # tokenize the XPath expression
      toks = xpath_lexer.scan(s)
      # add default prefix to unprefixed names
      toks2 = [_add_prefix(prefix, tok) for tok in toks]
      # build a string of the patched expression
      ls = [x.value for x in toks2]
      return ''.join(ls)
docs: Add `prefix` to all unprefixed names in `s`