FrameBox[box] displays with a frame drawn around box.
In StandardForm and InputForm, FrameBox is by default ignored, so that FrameBox[box] is interpreted just as box would be.
In StandardForm, explicit FrameBox objects are output literally. You can use DisplayForm to see the display form of such objects.
See Section 2.9.10.
See also: StyleBox, CellFrame, ColumnLines, RowLines.
New in Version 3.