[Before-Checkin trigger]

I would like to make a server-side trigger to check that any new check-in is going to have a name exceeding a length of characters.

I am able to make a simple trigger that prevents people from pushing anything to Plastic, but I do not know the syntax to make the simple length check, nor do I know where to host such a file.

Could someone please suggest the syntax needed to enforce this rule?

Is there somewhere in Plastic Cloud config where I can store such a file?

Thank you