code: @Nullable
      String next() {
          if( lastIdx >= selector.length() ) {
              return null;
          }
          LOOP: do {
              if( ++idx == selector.length() ) {
                  break LOOP;
              }
              switch( selector.charAt( idx ) ) {
                  case '.':
                  case '#':
                  case ':':
                  case '[':
                      break LOOP;
              }
          } while( true );
          String str = selector.substring( lastIdx, idx ).trim();
          lastIdx = idx;
          return str;
      }
docs: Get the next selector.
  @return the next or null