CREATE TYPE - Mailing list pgsql-sql

I want to create a data type that have tow arguments in the defenition,
like the varchar type:
create table mytmp(name varchar(10));

I like to do it like this:
create table mytmp(name myvarchar(10,"en_US"));

whow can it be done by "CREATE TYPE"
I want to implement the internal functions (compare, ...).
I faunded the documentation but I can't see any thing that help me to
create a type same as varchar( with argument)

Notice: I don't mean using "CREATE TYPE myvarchar AS( lenght integer,
collate char(10))

Thanks