android toolbar popupTheme vs theme

Question

Often I see this declaration of Toolbar in layout files:

<android.support.v7.widget.Toolbar
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="?attr/actionBarSize"
    app:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar"
    app:popupTheme="@style/ThemeOverlay.AppCompat.Light">
</android.support.v7.widget.Toolbar>

Why are there two attributes relating theming: theme and popupTheme?

What are the purposes of each of them?

Answer 1

1. popupTheme

   Specifies the theme to use when inflating popup menus. By default, uses the same theme as the Toolbar itself.

2. theme

   It is simply the theme of Toolbar.