src/vs/workbench/contrib/callHierarchy/common/callHierarchy.ts/CallHierarchyModel/fork
class CallHierarchyModel:	fork(item: CallHierarchyItem): CallHierarchyModel {
		const that = this;
		return new class extends CallHierarchyModel {
			constructor() {
				super(that.id, that.provider, [item], that.ref.acquire());
			}
		};
	}