If you add a @Tag attribute to a rule you must also add a package value to the top of your Compliance rule. This is required by the underlying Compliance technology, and has no functional implications.

A good practice for the package name is to use a unique value which identifies the group that owns (and is responsible for maintaining) the rule. All out-of-the-box rules have a set of suggested tags and a package name of data migrators datamigrators.