default:shortcode_attr and multiple values

Hello,
for a project I am massively using default:shortcode_attr for a huge form. The only problem: seems that in that mode, multiple values are not supported.

Example:
I have a multi checkboxes like this:
[checkbox* your-mood use_label_element default:shortcode_attr]
This is dinamically populated with values, for example
[1] => “happy”
[2] => “sad”
[3] => “medium”
[4] => “whatever”

I CAN set “sad” as default like this [contact-form-7 id="1859" title="My form" your-mood="2"]
but I CANNOT set multiple values. I tried multiple syntaxes but analyzing the code there is no string split of any kind.
Those examples that I tried but are NOT working:
[contact-form-7 id="1859" title="My form" your-mood="2_3"]
[contact-form-7 id="1859" title="My form" your-mood="2,3"]
[contact-form-7 id="1859" title="My form" your-mood="2" your-mood="3"]

Am I missing something?