Uh, I am wondering if it is just too details for our docs. Can you
think of some text and its location?
"Unique indexes on functions can be used to create special types of constraints, like considering unique values equal (coalesce) or only allowing a single unique integer value of a float column (floor). A filtered unique index only enforces uniqueness on the subset of rows that match the filter."
I guess this would append to the paragraph "When an index is declared unique, multiple table rows with equal indexed values are not allowed. Null values are not considered equal. A multicolumn unique index will only reject cases where all indexed columns are equal in multiple rows.". Links to the mentioned keywords and concepts would of course be helpful, but not strictly necessary.
I also thought of mentioning the caveat of (un)scannability of function or filtered indexes but maybe that is a bit much.
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- Tuomas