What is the purpose of the Android @Widget annotation?

What is the purpose of the Android @Widget annotation (defined in android / annotation / Widget.java )? I can't seem to find links to anything that might use it.

Edit: Yes, I read the description in the Javadoc. He does not explain the purpose of the annotation, that is, why he would like to use it. Is the class @Widget-annotated in some way considered somehow?