You can notify you cowriters when commenting by typing
@ then selecting a name from the dropdown (either with arrow keys or the mouse).
You will see
@[NAME] will be notified below if you select them through the dropdown. If not, they will not be notified (e.g. typing out their full-name without the dropdown will not work).
It will take a few minutes for the email notification to arrive – we wait for further comments and batch them into a single email instead of sending a notification for each one.