Array of strings when updating a field

Unintentionally discovered that following query works in PostgreSQL: UPDATE "sometable" SET "somefield" = ('string1', 'string2') WHERE "id" = 1; I'm passing an array of strings to field and the result is a string of '("string1","string2")', not an array as expected, at least then using php extension pgsql. How this happens and that does ('string1', 'string2') means in PostgreSQL? I don't think this works in other SQL RDBMSes.