public void add_parent (MiniObject parent)
parent as a parent for this.
Having one ore more parents affects the writability of this: if a
parent is not writable,
this is also not writable, regardless of its refcount. this is only writable
if all the parents are writable and its own refcount is exactly 1.
Note: This function does not take ownership of
parent and also does not take an additional reference. It is the responsibility of
the caller to remove the parent again at a later time.
a parent MiniObject