Custom text type for title text

I've frequently seen an issue in applications which store titles (eg of books, events, user profiles) where duplicate values are not properly vetted. 

The 'citext' type is helpful here, but I'd be keen to go further. 

I propose a 'titletext' type, which has the following properties when compared for equality:

 * Case insensitivity (like 'citext')

 * Only considers characters in [:alnum:] (that is, ignores spaces, punctuation, etc)

This would be useful for a range of situations where it's important to avoid entering duplicate values.

Given the discussion at https://www.postgresql.org/message-id/CAKFQuwY9u14TqG8Yzj%3DfAB0tydvvtK7ibgFEx3tegbPWsGjJpg%40mail.gmail.com I'd lean towards making this type not automatically coerce to text (to avoid surprising behaviour when comparing text to titletext).

Is a suitable patch likely to be accepted?

Thanks,

Daniel Heath