⟩ Explain How to create a signature over some content at a URL such that can change the URL without breaking the signature?
Use Reference in a Manifest to indicate the content by URI. Reference in Signature should indicate Manifest but should have transform that omits URI. Thus, URI can be changed without breaking signature.
NOTE: Core validation does not validate digest values in Manifest (only in SignedInfo), so the application must validate the Manifest after calling upon core validation.