In QV10 this was officially documented in the QVS manual. Not quite sure where it's gone in QV11, but you can give it a try:
Handing over a variable is imho only possible with IEPlugin; with AJAX you are only allowed to handover listbox-selections (or BookmarkIDs). May this helps in your situation. Syntax is similar to:
See page 232 in QV10SR1 Server Manual!