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diff --git a/src/UndoHistory.h b/src/UndoHistory.h
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+++ b/src/UndoHistory.h
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+// Scintilla source code edit control
+/** @file UndoHistory.h
+ ** Manages undo for the document.
+ **/
+// Copyright 1998-2024 by Neil Hodgson <neilh@scintilla.org>
+// The License.txt file describes the conditions under which this software may be distributed.
+
+#ifndef UNDOHISTORY_H
+#define UNDOHISTORY_H
+
+namespace Scintilla::Internal {
+
+/**
+ *
+ */
+class UndoHistory {
+	std::vector<Action> actions;
+	int maxAction;
+	int currentAction;
+	int undoSequenceDepth;
+	int savePoint;
+	int tentativePoint;
+	std::optional<int> detach;
+
+	void EnsureUndoRoom();
+
+public:
+	UndoHistory();
+
+	const char *AppendAction(ActionType at, Sci::Position position, const char *data, Sci::Position lengthData, bool &startSequence, bool mayCoalesce=true);
+
+	void BeginUndoAction();
+	void EndUndoAction();
+	void DropUndoSequence() noexcept;
+	void DeleteUndoHistory();
+
+	/// The save point is a marker in the undo stack where the container has stated that
+	/// the buffer was saved. Undo and redo can move over the save point.
+	void SetSavePoint() noexcept;
+	bool IsSavePoint() const noexcept;
+	bool BeforeSavePoint() const noexcept;
+	bool BeforeReachableSavePoint() const noexcept;
+	bool AfterSavePoint() const noexcept;
+	bool AfterDetachPoint() const noexcept;
+
+	// Tentative actions are used for input composition so that it can be undone cleanly
+	void TentativeStart() noexcept;
+	void TentativeCommit() noexcept;
+	bool TentativeActive() const noexcept;
+	int TentativeSteps() noexcept;
+
+	/// To perform an undo, StartUndo is called to retrieve the number of steps, then UndoStep is
+	/// called that many times. Similarly for redo.
+	bool CanUndo() const noexcept;
+	int StartUndo() noexcept;
+	const Action &GetUndoStep() const noexcept;
+	void CompletedUndoStep() noexcept;
+	bool CanRedo() const noexcept;
+	int StartRedo() noexcept;
+	const Action &GetRedoStep() const noexcept;
+	void CompletedRedoStep() noexcept;
+};
+
+}
+
+#endif