The place I would add them is in the example for multi-select problems. After having the most basic example for that kind of problem, I would include an example just like the one that I posted here, where the correct answers are code dependent instead of hard coded.
I have only been using WeBWorK for a month now. I really like it, but I have usually had to do a lot of experimenting to get the problems I've made to work correctly. I would definitely like to contribute the questions that I've made, and a tutorial showing how to design those questions. I plan on making tutorial videos at some point and posting them on a YouTube channel, but if WeBWorK has any documentation that includes examples, which I'm allowed to contribute to, I will gladly do that.