code: @Override
      public boolean contains(CharSequence s) {
          if (s instanceof FastStr) {
              return indexOf((FastStr) s) > -1;
          }
          return indexOf(s.toString()) > -1;
      }
docs: Wrapper of {@link String#contains(CharSequence)}
  
  @param s the char sequence to be found
  @return {@code true} if {@code s} has been found