Two matters with the same client are linked in billing. For example, payment plans are at the client level. The matters are also liked with respect to the participants in a matter. 

Also, when you pull up the contact’s “card”, the top has a tab for matters. It will show all matters in which the contact is linked. 

Could there be a way to reference “related matters” within the matter?

I do family law and we can often have a separate case number for the child support case, divorce or custody case, and any domestic violence or prior cases. We are required to list all related cases on pleadings so it’s just in a note right now, but it would be REALLY helpful to be able to link it so it’s clear (especially to staff who won’t necessarily recall it)