By now, you should be familiar with the basics of JointJS, as well as with some intermediate-difficulty topics.
The advanced section of the tutorial delves into much more detail about the topics mentioned in the basic and intermediate sections of the tutorial. Expect this section to grow in the future; we add advanced new features to JointJS regularly, and most of them will be introduced in this section. The current list of advanced topics can be found in the sidebar of this page.
We also provide an archive of additional advanced tutorials created for past versions of JointJS. They provide a wealth of information as well - with the disclaimer that they may no longer showcase the best/most optimized/easiest/cleanest way of doing things in the current version of JointJS. For guidance on current best practices, refer to the appropriate sections of the basic and intermediate tutorial.