I'm trying to add some custom content parsing in a TextBox using the PreviewKeyDown method (i'm just adding some text to the beginning of multiple lines and updating the selection position/length). However, whenever I make a change to the TextBox object, that event is being marked as "Significant" (from Java's UndoManager terminology, not sure what the correct term is in C#), or when time an undo is triggered, only that single event is being undone.
How do you mark undoable events as being "in-significant" so that multiple events can be undone each time an undo is triggered?
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