Обсуждение: [BUGS] seems column(alias_name) is a valid syntax? I cant find anythingalike in docs

Hi,

Sorry If bother you again for no reason. Was surprised by behaviour described in

Quite soon found out that column_name(alias_name) seems a valid syntax, below a(c) works - is it a feature? I could not find it anywhere in docs. 

s=# with c(a,b) as (values(1,2),(2,3))
select a(c),(c).a from c;a | a 
---+---1 | 12 | 2
(2 rows)

Why would I use such syntax in first place? as described in SO original post, he has a column named "count" and thus 

returns column "count" instead of number of rows. I can't tell why would you name column with function name.

So please help finding the docs and understanding why it works.

Thank you