Drill-down contextual filtering I've created a view called "Upcoming Events" that presents upcoming events in chronological order at the url /upcoming-events/all. Each event has associated tags. Currently my contextual filter is set so that replacing all in the url with a valid tag will present just events with that tag. Tags are set up as links with the url /upcoming-events/[field_tags]. 

My question is two-fold. How do I set up the contextual filter so that adding more tags on the end of the url (/upcoming-events/happy-hours/drupal/ for example) will further narrow the results presented to the user? Also, how do I set up the tag links to append the field tag to the end of the url rather than replace it?
If you click on More link under the contextual filter settings, there is an option to allow multiple values.

Enabling this option, you can use URLs like /upcoming-events/happy-hours,drupal to show events having both happy-hours and drupal tags.