Custom visuals are capable of using PowerBI's drill down.
Read more about Power BI drill down here
To support drill down in your visual, add a new field to "capabilities.json" named drilldown which has one property:
roles - the name of the dataRole you want to enable drill down on.
NOTE:
The drill down dataRole must be of 'Grouping' type.
"max" property in the dataRole conditions must be set to 1.
Once you add the role to drilldown, users can drag multiple fields into the data role.
example:
