Is is possible for Salesforce Duplicate Management matching rules to compare across objects?  

This article talks about cross-object duplicate rules:

https://focusonforce.com/configuration/native-duplicate-management-in-salesforce/

as does this Salesforce help page:

https://help.salesforce.com/articleView?id=duplicate_rules_overview.htm&type=5

When setting up matching rule criteria, there appears to be no way to select anything other than a field from the current object.

Is this a feature that needs to be enabled somehow or that existed and was withdrawn?