Linked credentials - what’s the vocabulary ?

Hi all 

I need to implement a trust chain of linked credentials 

https://www.w3.org/TR/vc-imp-guide/#referencing-other-credentials

Talks about hashlinks that reference a credential. But doesn’t give an example in a credential 

https://www.w3.org/TR/vc-data-model/#extensibility

Doesn’t say anything about how to say “this is a link to another vc”

Since the vc is an open model that accommodates any vocabulary (good thing), I can of course do it anyway I like 

But so that verifiers know how to find and follow links to related credentials , shouldn’t there be a standard vocabulary for specifying a linked credential ?

Kind regards 
Steven Capell
Mob: 0410 437854