Creating a listener for a custom mark tag?

@c-morten

In another issue you made this statement:

https://github.com/aws-samples/amazon-sumerian-hosts/issues/19

_"Another alternative would be to create your own message for the name of the mark tag and add a listener for that. Then you could use whatever logic you'd like to figure out which host you want to target inside your listener function."_

Can you give me a code snippet that shows me how to add a listener for a custom mark tag name and how from within that function I would target a particular host's charGaze location?