docs: def reghex(pattern):
      """
      Compile a regular hexpression (a short form regular expression subset
      specifically designed for searching for binary strings).
  
      A regular hexpression consists of hex tuples interspaced with control
      characters. The available control characters are:
  
      - ``?``: Any byte (optional).
      - ``.``: Any byte (required).
      - ``?{n}``: A set of 0 up to *n* bytes.
      - ``.{n}``: A set of exactly *n* bytes.
      - ``*``: Any number of bytes (or no bytes at all).
      - ``+``: Any number of bytes (at least one byte).
  
      Args:
          pattern(str): The reghex pattern.
  
      Returns:
          regexp: A regular expression as returned by ``re.compile()``.
      """
  
      if not reghex_check.match(pattern):
          raise SyntaxError('Invalid reghex pattern.')
  
      b_pattern = b''
  
      for match in reghex_regex.finditer(pattern):
          _, match_hex, _, match_char, match_char_len, match_star_plus = match.groups()
          if match_hex:
              b_pattern += re.escape(pwnypack.codec.dehex(match_hex))
          elif match_char:
              if match_char == '?':
                  if match_char_len is None:
                      b_pattern += b'.?'
                  else:
                      b_pattern += ('.{0,%d}?' % int(match_char_len[1:-1])).encode('ascii')
              else:
                  if match_char_len is None:
                      b_pattern += b'.'
                  else:
                      b_pattern += b'.' * int(match_char_len[1:-1])
          elif match_star_plus:
              b_pattern += b'.' + match_star_plus.encode('ascii') + b'?'
  
      try:
          return re.compile(b_pattern)
      except (TypeError, binascii.Error, re.error):
          raise SyntaxError('Invalid reghex pattern.')