Hi Experts:
I made a Sync. session between maintain session(main-session) and display session(sub-session). The number of records for display session(sub-session) may exceed the form limit(eg.Occurrences=6). But when I set the scrollbar status(fattr.scrollbar = true) in the script for the sub-session,When click on the vertical scrollbar of sub-session, the next.set action is performed on the main-session.
I think it's probably the control that's been transferred to the main-session through function witch.to.process(parent) (in the sub-session) at this point.(But the forms of the two sessions don't overlap!?)So how can I clicked vertical scrollbar on the sub-session and produce an action that only works on the sub-session?
Thanks for any suggestions!

When I did something like this I had to pass those specific events to the subsession. So the double arrows worked on the main session then the single arrows. I think in my case the bottom session was really the controlling session - then I passed the next set (etc) to the top session.

Yep bottom session was really the main session. Below snippet of code.

choice.next.view:
after.choice:
hold.rfq = tdexi010.rfqnum
export("hold.rfq", hold.rfq)
instruction = next.set
switch.to.process(process.exi0109,SWITCH.SAME.SIZE + SWITCH.WITHOUT.INTERACTION)
import("hold.rfq", hold.rfq)
tdexi010.rfqnum = hold.rfq
get.header.text()
execute(find.data)
execute(first.set)

When I did something like this I had to pass those specific events to the subsession. So the double arrows worked on the main session then the single arrows. I think in my case the bottom session was really the controlling session - then I passed the next set (etc) to the top session.

Thank you very much Mark, I did some tests, never found a good way to solve this problem, and finally I decided to give up this idea.
Thank you for your help!