in the external calendar CO, one has to give a URI, but it doesn't work with the html code of a google calendar.
It works with the ICAL link of google calendar, but some (repeated) items are displayed twice in the personal calendar.
Updated by dominique de guchtenaere almost 8 years ago
I used an ical link, and it works like a charm.
I tested it too with a html link: I didn't get a message (yet) it is the wrong format.
It's a bit confusing for a user:
Create - external calendar asks for a ical link
Import - ical asks for a file