Python factory_boy library m2m in Django model?

I'm currently using factory_boy for creating fixtures in my tests. Factory_boy docs only mentioned about SubFactory which could act like a ForeignKey field in a model. However, there was nothing on ManyToMany association. If I had a following Post model, how would I go about creating a factory for it?

class Post(models.Model):
    title = models.CharField(max_length=100)
    tags = models.ManyToManyField('tags.Tag')

class PostFactory(factory.Factory):
    FACTORY_FOR = Post

    title = 'My title'
    tags = ???