How to prefill Multiple Select in a form?

[Casey]

These approaches don’t seem to work:

foo=value1&foo=value2&foo=value3

foo[]=value1&foo[]=value2&foo[]=value3

Is there a way to do this?

[AlliAlosa · Accepted solution]

Try this: ?prefill_foo=value1,value2,value3

A quick test worked for me using that approach!