On: An introduction to Morphic: Self's UI toolkit

A more recent implementation of this is Morphic.js[0].

It powers Snap![1] which is the spiritual successor of Scratch 1.4 [2].

[0]: https://github.com/jmoenig/morphic.js/

[1]: https://snap.berkeley.edu/

[2]: https://scratch.mit.edu/scratch_1.4