Need to see more than one calendar at the same time

[prinzimaker]

First of all, I would like to thank you for this splendid library that greatly improves and speeds up my work.
Let me explain my problem: I need to display two calendars simultaneously, meaning I want to use two "calendar_id" at the same time, in order to see the events from one mixed with the events from the other.
However, when scheduling an appointment, I will obviously use only one of the two IDs.
I tried using an array or concatenating the strings of the two IDs separated by a comma and by a semicolon, but it doesn't work. It throwe an error.

So my question is: is it possible to do this, and if so, how?

Thank you very much in advance for your attention.
Aldo