code: func normalize(number string) string {
  	if VALID_ALPHA_PHONE_PATTERN.MatchString(number) {
  		return normalizeHelper(number, ALPHA_PHONE_MAPPINGS, true)
  	}
  	return NormalizeDigitsOnly(number)
  }
docs: // Normalizes a string of characters representing a phone number. This
  // performs the following conversions:
  //   - Punctuation is stripped.
  //   - For ALPHA/VANITY numbers:
  //     - Letters are converted to their numeric representation on a telephone
  //       keypad. The keypad used here is the one defined in ITU Recommendation
  //       E.161. This is only done if there are 3 or more letters in the
  //       number, to lessen the risk that such letters are typos.
  //
  //   - For other numbers:
  //     - Wide-ascii digits are converted to normal ASCII (European) digits.
  //     - Arabic-Indic numerals are converted to European numerals.
  //     - Spurious alpha characters are stripped.