A folderish type with ISelectableConstraintTypes behavior enabled allows any type to be pasted into, even if the type is otherwise disallowed via the folder_constraintypes_form.
- Type definition - all types are basically allowed - but this will be constrained via the object's constraint form (3rd screenshot):

2) ISelectableConstraintTypes enabled:

3) Constraint config:

- Pasted a folder into that type and that worked:

A folderish type with
ISelectableConstraintTypesbehavior enabled allows any type to be pasted into, even if the type is otherwise disallowed via thefolder_constraintypes_form.2) ISelectableConstraintTypes enabled:
3) Constraint config: