code: static double getPercent( Expression expression, CssFormatter formatter ) {
          double d = expression.doubleValue( formatter );
          if( expression.getDataType( formatter ) == Expression.PERCENT ) {
              d /= 100;
          } else if( d > 1.0 && d == (int)d ) {
              d /= 100;
          }
          return d;
      }
docs: Get the expression value as percent (range 0 - 1).
  
  @param expression
  the expression
  @param formatter
  current formatter
  @return the percent value