[MB_UST]

I figured it out, finally:
tell application "OmniFocus"
tell document 1
tell (first document window whose index is 1)
set SelectionV to selected trees of content
--Then you can parse the resulting variable (SelectionV) to get the data you want:
repeat with i from 1 to (count of SelectionV)
set ItemV to value of item i of SelectionV
end repeat
end tell
end tell
end tell