code: function controllersBoundTransclude(scope, cloneAttachFn, futureParentElement) {
            var transcludeControllers;
  
            // No scope passed in:
            if (!isScope(scope)) {
              futureParentElement = cloneAttachFn;
              cloneAttachFn = scope;
              scope = undefined;
            }
  
            if (hasElementTranscludeDirective) {
              transcludeControllers = elementControllers;
            }
            if (!futureParentElement) {
              futureParentElement = hasElementTranscludeDirective ? $element.parent() : $element;
            }
            return boundTranscludeFn(scope, cloneAttachFn, transcludeControllers, futureParentElement, scopeToChild);
          }
docs: This is the function that is injected as `$transclude`. Note: all arguments are optional!