code: @Override
      public Operation listValue( CssFormatter formatter ) {
          eval( formatter );
          if( type == LIST ) {
              Operation op = new Operation( this );
              for( Object obj : ((Collection)result) ) {
                  op.addOperand( new ValueExpression( this, obj ) );
              }
              return op;
          } else {
              return super.listValue( formatter );
          }
      }
docs: {@inheritDoc}