<!-- android:layout_martinTop="?attr/actionBarSize" moves adRelativeLayout below the appBarLayout, which otherwise would cover the top of mainWebView.
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"-->
<RelativeLayout
<!-- android:layout_martinTop="?attr/actionBarSize" moves adRelativeLayout below the appBarLayout, which otherwise would cover the top of mainWebView.
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"-->
<RelativeLayout