What does regclass signify in Postgresql

Question

I have the following line in a CREATE TABLE statement:

field1_id bigint DEFAULT nextval(\'table1_field1_id_seq\'::regclass) NOT NULL,

What does

Answer 1

From what I understand of the documentation, oid are subdivided in types. regclass are database objects representing relations (so that they belong to the metadata table pg_class).

It expresses a dependency between the sequence and the DEFAULT expression (meaning the process of producing a default value if no explicit value is provided in a INSERT query for instance), so that if one emits a DROP SEQUENCE ... on the sequence, the query won't pass, unless it's cascaded (by writing DROP SEQUENCE table1_field1_id_seq CASCADE).