src/vs/workbench/api/browser/mainThreadLanguageFeatures.ts/MainThreadLanguageFeatures/$registerDocumentSymbolProvider
class MainThreadLanguageFeatures:	$registerDocumentSymbolProvider(handle: number, selector: IDocumentFilterDto[], displayName: string): void {
		this._registrations.set(handle, this._languageFeaturesService.documentSymbolProvider.register(selector, <languages.DocumentSymbolProvider>{
			displayName,
			provideDocumentSymbols: (model: ITextModel, token: CancellationToken): Promise<languages.DocumentSymbol[] | undefined> => {
				return this._proxy.$provideDocumentSymbols(handle, model.uri, token);
			}
		}));
	}