Compound actions are just like simple actions but each action is separated by a semicolon:
Action: $Color="red";$Priority="high"
Sometimes, this leads to complications. Suppose, for example, you want an action to set the $OnAdd action. (Perhaps you have an agent that's looking for containers of $UrgentTasks, and wants to set the $OnAdd action for those containers). The simplest way of writing this is:
Action: $OnAdd=$Color="red";$Priority="high"
…which will do two things: set the $OnAdd action to "$Color=Red" and set the $Priority to high.
If you want the $OnAdd action to be set to the entire expression, enclose it in quotes:
Action: $OnAdd="$Color=red;$Priority=high"
The square bracketed style is also required if setting multiple $DisplayedAttributes values (or any List or Set-type attribute).
Action: $DisplayedAttributes=[Color;Name;Rule]
Action: $DisplayedAttributes= $DisplayedAttributes(parent) + [Border;AccentColor]
Previously, the latter used quoted strings but this is now deprecated.