How to just pop up a wait message window in rebol view?

I just want to popup a wait message window in rebol view, but there's no option to do so with View command as

View win: layout [text "wait"开发者_如何学JAVA]

do-some-lengthy-task

Unview win

will block the script until the user close the message himself which is not wanted here of course.

So how to make non-blocking view ?

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What about this?

View/new win: layout [button "Do-It" [print "ok"]]
repeat i 10 [print i wait 0:0:1] ;lengthy-task
Unview win

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fl: flash "Hang about .... "

do stuff...

unview/only fl