Sets whether the use of modifier keys should have an effect on the type of operation performed.
NO, if the user can tailor the drag operation by holding down a modifier key during the drag.
If this method is not implemented the default behavior is equivalent to returning
The dragging option that corresponds to the modifier key is combined with the source’s mask (as set with the
dragging method) using the C bitwise OR operator. See the description for the
dragging method in the
NSDragging protocol specification for more information about dragging masks and modifier keys.