code: function (less) {
  
          var Keyword = less.tree.Keyword;
          var DetachedRuleset = less.tree.DetachedRuleset;
  
          var isa = function (n, Type) {
              return (n instanceof Type) ? Keyword.True : Keyword.False;
          };
  
          if (!functions) {
              functions = {
                  isruleset: function (n) {
                      return isa(n, DetachedRuleset);
                  }
              };
          }
          return functions;
      }
docs: Get an instance of the plugin module
  @param {Object} less the less.js instance
  @return {Object} the functions to be injected