code: function verify_signature(file_data) {
    var match = PATTERN.exec(file_data);
    if (!match)
      return exports.SIGN_UNSIGNED;
    // Replace the signature with the TOKEN, then hash and see if it matches
    // the value in the file.  For backwards compatibility, also try with
    // OLDTOKEN if that doesn't match.
    var k, token, with_token, actual_md5, expected_md5 = match[1];
    for (k in TOKENS) {
      token = TOKENS[k];
      with_token = file_data.replace(PATTERN, '@'+'generated '+token);
      actual_md5 = md5_hash_hex(with_token, 'utf8');
      if (expected_md5 === actual_md5)
        return exports.SIGN_OK;
    }
    return exports.SIGN_INVALID;
  }
docs: Verify a file's signature.  @param  str  File contents as a string. @return      Returns SIGN_OK if the data contains a valid signature, SIGN_UNSIGNED if it contains no signature, or SIGN_INVALID if it contains an invalid signature.