Some questions regarding DID verification relationships

I've been reading up a bit on the current DID spec<https://www.w3.org/TR/did-core/>, and I’ve trouble understanding the ideas behind the verification relationships. The spec says that a verification relationship links the DID subject and a verification method (which consists amongst other of a controller property (to be specified as a DID)). Section 5.3<https://www.w3.org/TR/did-core/#verification-relationships> adds to this that verification relationships enable the associated verification methods to be used for different purposes, and its subsections specify properties, such as `authentication`, `assertionMethod` etc., that seem to be associated with a specific purpose, the actual workings of which is only hinted at.



Here are some questions I have:

  *   What’s the purpose of having a ‘controller’ in a verification method?
  *   What’s the role of the controller (how would verification work, given that the controller is represented by a DID that also has key material)?
  *   How does `assertionMethod` work to express claims, e.g. for issuing VCs (is that simply VC signing as an issuer)?
  *   Is there any text that is readable for non-implementers that documents these kinds of verification relationships, and explains how to extend the set of their types?



Rieks
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