register(fnCallback) {
			if (typeof fnCallback !== "function") {
				throw new Error('Registered callback must be a function.');
			}
			if (this.#allowMultiple) {
				this.#callbacks.push(fnCallback);
			} else {
				if (this.#callbacks) {
					throw new Error(`Callback is already registered. The hooks are restricted to the 'sap.ui.fl' library only.`);
				}

				this.#callbacks = fnCallback;
			}
		}
Registers a callback function for this hook.
@param {Function} fnCallback The callback to register.
@throws {Error} Throws an error if the callback is not a function.
@throws {Error} Throws an error if the callback is already registered for this hook.