Possible Values
copy allows the copy operation,
link allows the selection to be linked with the drop target
move allows the selection to be moved to the drop target
copyLink allows the copy or link operation,
depending on the target settings,
copyMove allows the copy or move operation,
depending on the target settings,
linkMove allows the link or move operation,
depending on the target settings,
all allows all drop effects),
none no drop effect is allowed and
the no-drop cursor is shown
uninitialized the default; the effectAllowed property
has not been initialized yet