Each calendar can have a default script. For example if you had 5 calendars you might want to set the text to be something different for each calendar.
Go to Calendar > Edit Calendars > Edit and change the option that says

Each calendar can have a default script. For example if you had 5 calendars you might want to set the text to be something different for each calendar.
Go to Calendar > Edit Calendars > Edit and change the option that says