I have successfully implemented the SPServices JQuery open source solution but unfortunately it doesn't seem to support multi select fields (I mean the ones where you can enable "allow multiple values"). Can you suggest another Library (possibily but unlikely free) that can achieve that result? Or, even better, is there any way to achieve that directly in Sharepoint (perhaps through Sharepoint Designer)? I find hard to believe that Sharepoint 2013 doesn't support that kind of feature yet.
FYI I am working with Sharepoint Foundation 2013 and Sharepoint Designer 2013.