code: private int maxOperadType( CssFormatter formatter ) {
          int dataType = operands.get( 0 ).getDataType( formatter );
          for( int i = 1; i < operands.size(); i++ ) {
              dataType = Math.max( dataType, operands.get( i ).getDataType( formatter ) );
          }
          return dataType;
      }
docs: Get the highest data type of different operands
  @param formatter current formatter
  @return the data type