Introduce :paramref:`_orm.relationship.sync_backref` flag in a relationship
to control if the synchronization events that mutate the in-Python
- attributes are added. This flag is implied in a ``viewonly=True``
- relationship. This supersedes the previous change :ticket:`5149`, which
- warned that ``viewonly=True`` relationship target of a back_populates or
- backref configuration would be disallowed.
+ attributes are added. This supersedes the previous change :ticket:`5149`,
+ which warned that ``viewonly=True`` relationship target of a
+ back_populates or backref configuration would be disallowed.