-<!-- android:layout_martinTop="?attr/actionBarSize" moves the RelativeLayout below the appBarLayout, which otherwise would cover the top of mainWebView. -->
-<!-- the RelativeLayout has an id of adView in the standard flavor so that the ad commands (which do nothing in the standard flavor) don't produce errors. -->
+<!-- android:layout_martinTop="?attr/actionBarSize" moves the RelativeLayout below the appBarLayout, which otherwise would cover the top of mainWebView.
+ the RelativeLayout has an id of adView in the standard flavor so that the ad commands (which do nothing in the standard flavor) don't produce errors.
+ android:layout_weight="1" sets the RelativeLayout to fill the rest of the screen because it is encapsulated in a LinearLayout with android:orientation="vertical". -->