Обсуждение: Describe UNION's cast on derived table

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/10/static/typeconv-union-case.html
Description:

Hi!

Whilst the type conversion works great on the query ;select 10 as col1 union
select null as col1;, it does not on the almost same one ;select col1 from
(select 10 as col1) t1 union select col1 from (select null as col1) t2;,
giving the error "UNION types integer and text cannot be matched". I'm using
a 64-bit PostgreSQL 10.1 on linux.

Please, describe this situation better on the docs. Thank you so much.