Because there is no set type in PostgreSQL I had to use domain. I have named a domain gender. It is text type. Then in users table I have created a column with that gender type. Now, how is stored the gender in the users table? As text or binary?
Domain type is based on some basic "buildin" type always. This type specifies a binary format. So if your domain is based on "text" type, then you store data as text.