docs(combineAll): Update docs for combineAll (ReactiveX#4035)

src/internal/operators/combineAll.ts

@@ -6,6 +6,50 @@ export function combineAll<T>(): OperatorFunction<ObservableInput<T>, T[]>;
 export function combineAll<T>(): OperatorFunction<any, T[]>;
 export function combineAll<T, R>(project: (...values: T[]) => R): OperatorFunction<ObservableInput<T>, R>;
 export function combineAll<R>(project: (...values: Array<any>) => R): OperatorFunction<any, R>;
+/**
+ * Flattens an Observable-of-Observables by applying {@link combineLatest} when the Observable-of-Observables completes.
+ *
+ * ![](combineAll.png)
+ *
+ * `combineAll` takes an Observable of Observables, and collects all Observables from it. Once the outer Observable completes,
+ * it subscribes to all collected Observables and combines their values using the {@link combineLatest}</a> strategy, such that:
+ *
+ * * Every time an inner Observable emits, the output Observable emits
+ * * When the returned observable emits, it emits all of the latest values by:
+ *    * If a `project` function is provided, it is called with each recent value from each inner Observable in whatever order they
+ *      arrived, and the result of the `project` function is what is emitted by the output Observable.
+ *    * If there is no `project` function, an array of all the most recent values is emitted by the output Observable.
+ *
+ * ---
+ *
+ * ## Examples
+ * ### Map two click events to a finite interval Observable, then apply `combineAll`
+ * ```javascript
+ * import { map, combineAll, take } from 'rxjs/operators';
+ * import { fromEvent } from 'rxjs/observable/fromEvent';
+ *
+ * const clicks = fromEvent(document, 'click');
+ * const higherOrder = clicks.pipe(
+ *   map(ev =>
+ *      interval(Math.random() * 2000).pipe(take(3))
+ *   ),
+ *   take(2)
+ * );
+ * const result = higherOrder.pipe(
+ *   combineAll()
+ * );
+ *
+ * result.subscribe(x => console.log(x));
+ * ```
+ *
+ * @see {@link combineLatest}
+ * @see {@link mergeAll}
+ *
+ * @param {function(...values: Array<any>)} An optional function to map the most recent values from each inner Observable into a new result.
+ * Takes each of the most recent values from each collected inner Observable as arguments, in order.
+ * @return {Observable<T>}
+ * @name combineAll
+ */
 export function combineAll<T, R>(project?: (...values: Array<any>) => R): OperatorFunction<T, R> {
   return (source: Observable<T>) => source.lift(new CombineLatestOperator(project));
 }