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$Post$PreRead

$PrePrint

FilledSmallSquare$PrePrint is a global variable whose value, if set, is applied to every expression before it is printed.

FilledSmallSquare$PrePrint is applied after Out[n] is assigned, but before the output result is printed.

FilledSmallSquare See The Mathematica Book: Section 2.13.1.

FilledSmallSquare See also: $Post, $MessagePrePrint.

Further Examples

$Post$PreRead