Curly braces in T-SQL

I've come across the following t-sql:

SELECT {d'9999-12-31'}

Which returns 9999-12-31 00:00:00.000.

This seems to be converting the type of the string literal to a DATETIME. I can't find any documentation on this syntax and I'm wondering if there are any variations, for example if I have a literal 1 but want to represent this in a BIGINT without using CONVERT()/CAST().

Can anyone provide any further information on this syntax? Thanks.