public override bool CanMerge(DocumentUndoAction action) { if (!(action is UndoMyEditAction)) { return(false); } var action_casted = (UndoMyEditAction)action; if (!(action_casted.__UndoAction is UndoTextEnter)) { return(false); } return(__UndoAction.CanBeMergedWith((UndoTextEnter)(action_casted.__UndoAction))); }