Automata by Example – build cellular automata just by clicking around

From the writeup, for those that wonder like me what's happening:

The technique, which I think of as rule generation, is something a little like direct manipulation, but with an additional generalisation step. You click the pixel you want, but instead of just setting the pixel directly, the system figures out a rule that would set that pixel and applies that rule globally. In other words, you determine the rule from the action, then use the rule to apply more actions.

https://samgentle.com/posts/2017-01-14-automata-by-example