Playing with interactions in STACK exercises

By using question behaviors with multiple tries, we bring more interactivity into STACK tasks. On the front end side, besides using JSXGraph as a tool to try out and explore, we also work with additional small JavaScript snippets. On the back end side, we make heavy use of the possibilities to work with strings generating HTML code. As a result, we get new variants of using STACK as a learning environment that positively influence student understanding.