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?

Solution

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.