More on drill-down

[cpsievert]

Add an example of drilling down in a single view, like https://edgarruiz.shinyapps.io/db-dashboard/

Also, now that we have sunburst, would be nice to mention this 'native' drill-down ability, and how it can be linked to other views

[cpsievert]

Might also make sense to add an example to the JavaScript section (drill-down on a bar chart via customdata)