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DialogSymbols$Pre

DialogProlog

FilledSmallSquareDialogProlog is an option for Dialog which can give an expression to evaluate before the dialog starts.

FilledSmallSquare You must use a delayed rule of the form DialogProlog :> expr to prevent expr from evaluating prematurely.

FilledSmallSquare Expressions given by DialogProlog are evaluated after symbol values are localized, and before any expression given as the argument of Dialog is evaluated.

FilledSmallSquare See The Mathematica Book: Section 2.13.2.

FilledSmallSquare See also: $Epilog.

DialogSymbols$Pre