XYplotx Plot Annotation
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       * To add a label, pointer, or rectangle to the plot:

            1. press shift-button-3 down at one corner of the pointer
               or rectangle to be drawn (or any point if only a label
               is to be drawn).

            2. hold button down and move to the opposite corner of the
               pointer or rectangle.

            3. release shift-button-3.
               A dialog box appears with fields to enter label text,
               and radio boxes to select line-segment, pointer, or rectangle.

       * To erase a label:

            1. press shift-button-1 down at one corner of a region surrounding
               the label to be erased.

            2. hold button down and move to the opposite corner of the
               erase region.

            3. release shift-button-1.
               after release, any markers within the erase box are removed.