Change CLIENT_ENCODING to client_encoding plus a question on "SET NAMES"

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/13/multibyte.html
Description:

Here is a tiny modification at [1] (change CLIENT_ENCODING to lowercase): 
-SET CLIENT_ENCODING TO 'value';
+SET client_encoding TO 'value';

Besides that, please allow me ask a question. 
The PG doc at[1] said "you can use the standard SQL syntax SET NAMES for
this purpose", and it works. But no PG help-doc describes this SQL syntax of
"SET NAMES".
Is it on purpose or missed? I'd be grateful if anyone can share me the rule
on whether or not to add a SQL syntax in PG help-doc.

[1]https://www.postgresql.org/docs/13/multibyte.html