From b6819fe9bb1b43e8bbbc4265bb25b4a689596091 Mon Sep 17 00:00:00 2001
From: Judy Bogart <jbogart@gmail.com>
Date: Wed, 16 Jan 2019 14:25:28 -0800
Subject: [PATCH] docs: add inpur vars doc (#27377)

PR Close #27377
---
 packages/common/src/directives/ng_for_of.ts       | 15 ++++++++++++++-
 .../change_detection/differs/iterable_differs.ts  |  8 ++++++--
 2 files changed, 20 insertions(+), 3 deletions(-)

diff --git a/packages/common/src/directives/ng_for_of.ts b/packages/common/src/directives/ng_for_of.ts
index 6fffe6e357..df197fb722 100644
--- a/packages/common/src/directives/ng_for_of.ts
+++ b/packages/common/src/directives/ng_for_of.ts
@@ -31,7 +31,7 @@ export class NgForOfContext<T> {
  * The directive is placed on an element, which becomes the parent
  * of the cloned templates.
  *
- * The `ngForOf` is generally used in the
+ * The `ngForOf` directive is generally used in the
  * [shorthand form](guide/structural-directives#the-asterisk--prefix) `*ngFor`.
  * In this form, the template to be rendered for each iteration is the content
  * of an anchor element containing the directive.
@@ -124,11 +124,19 @@ export class NgForOfContext<T> {
  */
 @Directive({selector: '[ngFor][ngForOf]'})
 export class NgForOf<T> implements DoCheck {
+  /**
+   * The value of the iterable expression, which can be used as a
+   * [template input variable](guide/structural-directives#template-input-variable).
+   */
   @Input()
   set ngForOf(ngForOf: NgIterable<T>) {
     this._ngForOf = ngForOf;
     this._ngForOfDirty = true;
   }
+  /**
+   * A function that customizes the default tracking algorithm.
+   * When supplied, Angular tracks changes by the return value of the function.
+   */
   @Input()
   set ngForTrackBy(fn: TrackByFunction<T>) {
     if (isDevMode() && fn != null && typeof fn !== 'function') {
@@ -155,6 +163,11 @@ export class NgForOf<T> implements DoCheck {
       private _viewContainer: ViewContainerRef, private _template: TemplateRef<NgForOfContext<T>>,
       private _differs: IterableDiffers) {}
 
+  /**
+   * The [template reference variable](guide/template-syntax#template-reference-variables--var-)
+   * for the expanded directive.
+   * Compare [template input variable](guide/structural-directives#template-input-variable)
+   */
   @Input()
   set ngForTemplate(value: TemplateRef<NgForOfContext<T>>) {
     // TODO(TS2.1): make TemplateRef<Partial<NgForRowOf<T>>> once we move to TS v2.1
diff --git a/packages/core/src/change_detection/differs/iterable_differs.ts b/packages/core/src/change_detection/differs/iterable_differs.ts
index 4fae01f8d9..8166bc4746 100644
--- a/packages/core/src/change_detection/differs/iterable_differs.ts
+++ b/packages/core/src/change_detection/differs/iterable_differs.ts
@@ -117,8 +117,12 @@ export interface IterableChangeRecord<V> {
 export interface CollectionChangeRecord<V> extends IterableChangeRecord<V> {}
 
 /**
- * An optional function passed into {@link NgForOf} that defines how to track
- * items in an iterable (e.g. fby index or id)
+ * An optional function passed into the `NgForOf` directive that defines how to track
+ * changes for items in an iterable.
+ * When supplied, Angular tracks changes by the return value of the function.
+ * @param index The iteration index.
+ * @param item The item ID.
+ * @return The value to use for tracking changes.
  *
  * @publicApi
  */