How to put appwidget-provider declaration for android widget

I am studying android's sample Wiktonary in how to create a widget for android.

My questions is why it puts

<appwidget-provider xmlns:android="http://schemas.android.com/apk/res/android"
    android:minWidth="146dip"
    android:minHeight="72dip"
    android:updatePeriodMillis="86400000"
    android:initialLayout="@layout/widget_message" />

in a file called wdiget_word.xml under res/xml? Instead of putting it under AndroidMa开发者_StackOverflow中文版nifest file?

Because that is what you are supposed to do.