src/vs/base/parts/quickinput/browser/quickInput.ts/QuickPick/handleAccept
class QuickPick:	private handleAccept(inBackground: boolean): void {

		// Figure out veto via `onWillAccept` event
		let veto = false;
		this.onWillAcceptEmitter.fire({ veto: () => veto = true });

		// Continue with `onDidAccpet` if no veto
		if (!veto) {
			this.onDidAcceptEmitter.fire({ inBackground });
		}
	}