This is an action object where, per its description, writing the port number of an L4 entry deletes the matching Layer 4 user-group membership entry keyed by that port. Admins use this to remove a port-to-group mapping, for example when a service is decommissioned and its traffic should no longer be filtered as part of that user group. For example, writing 80 here deletes the L4 membership entry for port 80, removing HTTP traffic's group assignment.