Aha, it's quite possible it worked before I commented, but it doesn't change the URLs as you click on the checkboxes so I couldn't tell.

I cannot guess the URLs for combinations of checkboxes, e.g. canvas+charting.

Currently there is no URL structure for more than one category... but now there will be. Thanks for the idea!

Completely off topic but just thought I'd say hi as a fellow nilliams :) HI!