Requirements for Validation Battle.net Tag

What are the requirements for validation a Battle.net Tag? (Rules, Limits, etc)

I want to add some validation to my app that if a invalid Battle.net Tag was entered it will throw an error and not make the API request.

Found the solution for those that are still looking here it is:

$pattern = '/^[\p{L}\p{Mn}][\p{L}\p{Mn}0-9]{2,11}-[0-9]{4,5}+$/u';