Canon mx860 - Manual (Page 293)

Important
Staple Side and Specify Margin... appear grayed out and are unavailable when:
Poster or Booklet is selected for Page Layout.
Scaled is selected for Page Layout (If Duplex Printing is also selected, only Staple Side is
selectable).
Borderless is selected for Page Layout.
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Page 293 of 997 pages Setting the Stapling Margin