I think the information about the "order of execution" when checking CHECK constraints when inserting or updating records is missing in the documentation.
Check constraints require immutable functions and do not have side effects. The order of their execution is immaterial and thus not documented. The server is free to do whatever it wishes whenever it wishes and users should not depend on any specific observed order in their usage (I don't believe we actually say to avoid depending upon undocumented behavior but that is the general guideline or working with systems).