code: function(nvalue){
        if(!!nvalue){
          if(alternate) combine.destroy(alternate)
          if(ast.consequent) consequent = self.$compile(ast.consequent, {
            record: true,
            element: options.element ,
            extra:extra
          });
        }else{
          if( consequent ) combine.destroy(consequent)
          if( ast.alternate ) alternate = self.$compile(ast.alternate, {record: true, element: options.element, extra: extra});
        }
      }
docs: attribute inteplation