The second parameter of the cb function is similar to the second parameter of the original MessageBox (I won't explain its meaning; there's documentation for that). The second parameter is optional; you can omit it.
Okay, then, the next question. "Cascading task." Let's say we need to capture 3 different mines: a sawmill, an ore mine, and a sulfur mine. What's the best way to structure this? Should we set up 3 checks and change the task status after each one, or what? Or should we use a trigger that checks, for example, every day, whether we have that mine?