Where should 'app:layout_behavior' be set?

Check this link: https://developer.android.com/reference/android/support/design/widget/AppBarLayout.html

AppBarLayout also requires a separate scrolling sibling in order to know when to scroll. The binding is done through the AppBarLayout.ScrollingViewBehavior class, meaning that you should set your scrolling view's behavior to be an instance of AppBarLayout.ScrollingViewBehavior. A string resource containing the full class name is available.

They mentioned about that, it should be the View which will be shown under the AppBarLayout like this:

<android.support.design.widget.CoordinatorLayout
         xmlns:android="http://schemas.android.com/apk/res/android"
         xmlns:app="http://schemas.android.com/apk/res-auto"
         android:layout_width="match_parent"
         android:layout_height="match_parent">

     <android.support.v4.widget.NestedScrollView
             android:layout_width="match_parent"
             android:layout_height="match_parent"
             app:layout_behavior="@string/appbar_scrolling_view_behavior">

         <!-- Your scrolling content -->

     </android.support.v4.widget.NestedScrollView>

     <android.support.design.widget.AppBarLayout
             android:layout_height="wrap_content"
             android:layout_width="match_parent">

         <android.support.v7.widget.Toolbar
                 ...
                 app:layout_scrollFlags="scroll|enterAlways"/>

         <android.support.design.widget.TabLayout
                 ...
                 app:layout_scrollFlags="scroll|enterAlways"/>

     </android.support.design.widget.AppBarLayout>

 </android.support.design.widget.CoordinatorLayout>

---

My question is: in what exact ViewGroup (or maybe View) should we put that app:layout_behavior?

And in this link: http://guides.codepath.com/android/Handling-Scrolls-with-CoordinatorLayout

Next, we need to define an association between the AppBarLayout and the View that will be scrolled. Add an app:layout_behavior to a RecyclerView or any other View capable of nested scrolling such as NestedScrollView. The support library contains a special string resource @string/appbar_scrolling_view_behavior that maps to AppBarLayout.ScrollingViewBehavior, which is used to notify the AppBarLayout when scroll events occur on this particular view. The behavior must be established on the view that triggers the event.

Make sure you added the appbar_scrolling_view_behavior field in your String.xml

<!-- The class name to the ScrollingChildBehavior required for AppBarLayout -->
<string name="appbar_scrolling_view_behavior" translatable="false">android.support.design.widget.AppBarLayout$ScrollingViewBehavior</string>

And as everyone knows we just can use this like below

<android.support.v7.widget.RecyclerView
        android:id="@+id/rvSomeList"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        app:layout_behavior="@string/appbar_scrolling_view_behavior" />

Its just for info not OP answer.

app:layout_behavior should be set to those views which are direct child of Coordinator layout