Or to try and explain that better... It's not a chart library, but a framework for wiring up dynamic data to collections of DOM nodes (either HTML or SVG) in any way you like. eg you can write specific chart libraries using it.
It is oriented around the lifecycles of instances of data - eg entry and exit hooks to run as data appears and disappears, and it has a lot of powerful lower level functionality.
It's not so much for people wanting to make new 'instances' of a visualisation. It's more for people wanting to make new 'classes' of visualisations.