"""
`m2m_changed`
```
def m2m_signals_handler(action, instance, reverse, model, pk_set, using):
pass
PRE_ADD = 'pre_add'
POST_ADD = 'post_add'
PRE_REMOVE = 'pre_remove'
POST_REMOVE = 'post_remove'
PRE_CLEAR = 'pre_clear'
POST_CLEAR = 'post_clear'
