code: void appendPropertiesTo( CssFormatter formatter ) {
          if( properties.isEmpty() ) {
              return;
          }
          formatter.addVariables( variables );
          for( Formattable prop : properties ) {
              switch( prop.getType() ) {
                  case Formattable.RULE:
                      Rule rule = (Rule)prop;
                      // inline rules
                      if( rule.isValidCSS( formatter ) && rule.isInlineRule( formatter) ) {
                          rule.appendPropertiesTo( formatter );
                      }
                      break;
                  default:
                      prop.appendTo( formatter );
              }
          }
          formatter.removeVariables( variables );
      }
docs: Append the properties of the rule.
  
  @param formatter current formatter