Implementing custom Visitors

I'm trying to make usage of the visitor patterns for a project. Just by declaring a Custom visitor, I can see it being registered but I have no idea how to make it visible to the graphene flow so it get's called and runs my enter/leave methods. any help is appreciated.

Thanks

Edit: This added the wrong label as I might have started this in the wrong place. Was trying to change the label to "HELP_NEEDED" but I can't seem to be able to do it. Sorry