docs: public static int countMatches(final CharSequence str, final CharSequence sub) {
          if (isEmpty(str) || isEmpty(sub)) {
              return 0;
          }
          int count = 0;
          int idx = 0;
          while ((idx = CharSequenceUtils.indexOf(str, sub, idx)) != INDEX_NOT_FOUND) {
              count++;
              idx += sub.length();
          }
          return count;
      }