[NOVICE] opr_charset rule in gram.y

I was going through the grammer rule for Character types in gram.y and found an optional sub rule in is "opt_charset"

CharacterWithLength:  character '(' Iconst ')' opt_charset

{

            if (($5 != NULL) && (strcmp($5, "sql_text") != 0))

                    $1 = psprintf("%s_%s", $1, $5);

           

            $$ = SystemTypeName($1);

I would like to understand how opt_charset would get used in real applications. I tried to make use of it but results in failure:

postgres=# create table testchar (c1 char(5) character set utf8);

ERROR:  type "pg_catalog.bpchar_utf8" does not exist

LINE 1: create table testchar (c1 char(5) character set utf8);

There does not seem to be any documentation available about this optional parameter in the documents for Character data type( at least I could not find any).

Any inputs on this are appreciated.

Regards,

Neha