..."This is because the SQL standard requires constraint names to be unique within a schema, but PostgreSQL does not enforce this restriction." ... PostgreSQL does enforce unique constraint names in a schema:
[...] ... but I guess this is not what the notes is supposed to tell me, correct?
Practically speaking there must be some level of scope where a duplicate name error can occur. All the docs say is that the schema scope is not it. You've demonstrated that it is the table scope where duplication of names is detected.
