Let's say we have a bloger which can assign from one to five tags to his blog. While submiting the server should count tags and check whether the collection in the allowed range. It can be done with Choice validator and min and max options. But in this case we have such problems:

• It should fetch all tags from db to check that choices are valid,
• Very hard to define callback in case of using $repository->findAll()

From another side we have Min\Max and MinLength\MaxLength validators but they very restrictive (the first takes only integers and second one only strings)

So I am thinking of moving count validation rules from Choice to a new validators called MinCount and MaxCount

BTW I can do a PR if you find it useful.