What does the "summary" sink do?

Questions
1

The main screen component has some obvious sinks including title (documented) and subtitle (currently undocumented).

I noticed there is a sink there called summary but could not easily see work out what it does.

Does anyone have any insights on its purpose?

2

Summary is part of our accessibility features. Unless you’re adding accessibility to your activities it won’t be of any use to you.

3

Makes sense, thanks.