docs: def technical_words_from_shadow_contents(shadow_contents):
      """Get a set of technical words from :shadow_contents:.
  
      :shadow_contents: is an array of shadow contents, as returned by
      spellcheckable_and_shadow_contents.
      """
      technical_words = set()
      for line in shadow_contents:
          # "Fix up" the shadow line by replacing zeros with spaces.
          line = "".join([(lambda c: " " if c == 0 else c)(c) for c in line])
          for sym in _split_into_symbol_words(line):
              if len(sym) and re.compile(_VALID_SYMBOL_WORDS).match(sym):
                  technical_words |= set([sym])
  
      return technical_words