I like to learn German from the instructions given in class and one such instruction was presented below:
Wenn du Informationen darüber hinzufügen möchtest, wer die Handlung ausführt, kannst du von (+ Dativ) verwenden.
Now, I understand this sentence means roughly:
When you want to add information about who did the action, you can use von + dative.
But the part
Wenn du Informationen darüber hinzufügen möchtest, wer die Handlung ausführt
bothers me as I can't sense why there is the need for a comma between "möchtest" and "wer".
Is there a reason for this? What kind of clause is being presented in this situation?