docs: private int postBasicCategoryIndex(String category) {
      boolean sawAtZero = false;
      char seenAtZero = '\u0000';
      int i = 0;
      for (int leng = category.length(); i < leng; i++) {
        char ch = category.charAt(i);
        if (isLabelAnnotationIntroducingCharacter(ch)) {
          if (i == 0) {
            sawAtZero = true;
            seenAtZero = ch;
          } else if (sawAtZero && i > 1 && ch == seenAtZero) {
            sawAtZero = false;
          } else {
            break;
          }
        }
      }
      return i;
    }