All caps types can include numerics

[bradyt]

From yaml/lib/src/scanner.dart, the numerals in for example NUMBER_9 should be fontified as constant, but is not.

  bool get _isTagChar {
    var char = _scanner.peekChar();
    if (char == null) return false;
    switch (char) {
      case HYPHEN:
      case SEMICOLON:
      case SLASH:
      case COLON:
      case AT:
      case AMPERSAND:
      case EQUALS:
      case PLUS:
      case DOLLAR:
      case PERIOD:
      case TILDE:
      case QUESTION:
      case ASTERISK:
      case SINGLE_QUOTE:
      case LEFT_PAREN:
      case RIGHT_PAREN:
      case PERCENT:
        return true;
      default:
        return (char >= NUMBER_0 && char <= NUMBER_9) ||
            (char >= LETTER_A && char <= LETTER_Z) ||
            (char >= LETTER_CAP_A && char <= LETTER_CAP_Z);
    }
  }