What is the role of the namespace used with prefersDefaultFocus?

I'm not understanding the role of the namespace used with prefersDefaultFocus.

If I use prefersDefaultFocus, how would I choose the view where the namespace is defined? What could go wrong if I chose the "wrong" place?

I am most interested in understanding how this feature behaves on macOS.

What is the role of the namespace used with prefersDefaultFocus?
 
 
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