Strong references satisfy requirement 3.1.11that it be possible to request creation of a referential member for which the server guarantees referential integrity.
DAV:refintegrity = “T” for strong references. Satisfies requirement 3.1.13 that it be possible to discover whether a referential member is strong or weak.
To support this guarantee, the target resource has a DAV:refsource property whose value is a list of the URIs of all strong references to it. This property also satisfies requirement 3.1.14 that it be possible to discover whether a resource is the target of a strong reference.