src/vs/workbench/contrib/notebook/browser/notebook.contribution.ts/SimpleNotebookWorkingCopyEditorHandler/_installHandler
class SimpleNotebookWorkingCopyEditorHandler:	private async _installHandler(): Promise<void> {
		await this._extensionService.whenInstalledExtensionsRegistered();

		this._register(this._workingCopyEditorService.registerHandler({
			handles: workingCopy => typeof this._getViewType(workingCopy) === 'string',
			isOpen: (workingCopy, editor) => editor instanceof NotebookEditorInput && editor.viewType === this._getViewType(workingCopy) && isEqual(workingCopy.resource, editor.resource),
			createEditor: workingCopy => NotebookEditorInput.create(this._instantiationService, workingCopy.resource, this._getViewType(workingCopy)!)
		}));
	}