I was tasked with adding this to an existing view and the README was not clear.
The reference to "type" in the filter had me confused as the "Selective" option did not appear in the "Filter type to expose" radio buttons on the field I was wanting to make selective. One of our team members knew what to expect from the module though and when pointed out it was obvious and intuitive.
A little more detail in the README would remove this confusion.
Needs work
1.0
Documentation
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
Thanks for taking the time to make it easier for people to understand how to use this!
I'm using a variation of your suggestion in the Backdrop version -- the only change I think would be needed here is that you've used the word "prefix" in a few locations but the "(selective)" text is actually added as a suffix.