This resource should be part of FHIR as citations are common in reports and a formal representation of a citation is useful.
Support for adding citations to Compositions, DiagnosticReports and annotations is needed. Not just as reference but also as hyperlinks from strings/markdown.
How this is done defined in the Citation resource and referred to from these resources and datatypes.
Such reference should be possible to individual Citation resources as well as to Lists of Citation resources and DocumentReferences.