The LDP specification makes DELETE optional. For a Solid server implementing DELETE, what, if any, constraints are on delete?

Specifically, can a client DELETE a non-empty container? If so, is that request recursive? Does the presence of contained resources affect the value of the Allow response header? If a DELETE operation is attempted on a non-empty container (and the request is rejected), is there a recommended ldp:constrainedBy relation that a server should use to inform a client why the request failed?