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diff --git a/src/xml/event.h b/src/xml/event.h
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+// SPDX-License-Identifier: GPL-2.0-or-later
+/** @file
+ * @brief Event object representing a change of the XML document
+ *//*
+ * Authors:
+ *   Unknown author(s)
+ *   Krzysztof Kosiński <tweenk.pl@gmail.com> (documentation)
+ *
+ * Copyright (C) 2018 Authors
+ * Released under GNU GPL v2+, read the file 'COPYING' for more information.
+ */
+
+#ifndef SEEN_INKSCAPE_XML_SP_REPR_ACTION_H
+#define SEEN_INKSCAPE_XML_SP_REPR_ACTION_H
+
+typedef unsigned int GQuark;
+#include <glibmm/ustring.h>
+
+#include <iterator>
+#include "util/share.h"
+#include "util/forward-pointer-iterator.h"
+#include "inkgc/gc-managed.h"
+#include "xml/node.h"
+
+namespace Inkscape {
+namespace XML {
+
+/**
+ * @brief Enumeration of all XML event types
+ */
+// enum EventType {
+//     EVENT_ADD, ///< Child added
+//     EVENT_DEL, ///< Child removed
+//     EVENT_CHG_ATTR, ///< Attribute changed
+//     EVENT_CHG_CONTENT, ///< Content changed
+//     EVENT_CHG_ORDER ///< Order of children changed
+// };
+
+/**
+ * @brief Generic XML modification event
+ *
+ * This is the base class for all other modification events. It is actually a singly-linked
+ * list of events, called an event chain or an event log. Logs of events that happened
+ * in a transaction can be obtained from Document::commitUndoable(). Events can be replayed
+ * to a NodeObserver, or undone (which is equivalent to replaying opposite events in reverse
+ * order).
+ *
+ * Event logs are built by appending to the front, so by walking the list one iterates over
+ * the events in reverse chronological order.
+ */
+class Event
+: public Inkscape::GC::Managed<Inkscape::GC::SCANNED, Inkscape::GC::MANUAL>
+{
+public:        
+    virtual ~Event() = default;
+
+    /**
+     * @brief Pointer to the next event in the event chain
+     * 
+     * Note that the event this pointer points to actually happened before this event.
+     * This is because the event log is built by appending to the front.
+     */
+    Event *next;
+    /**
+     * @brief Serial number of the event, not used at the moment
+     */
+    int serial;
+    /**
+     * @brief Pointer to the node that was the object of the event
+     *
+     * Because the nodes are garbage-collected, this pointer guarantees that the node
+     * will stay in memory as long as the event does. This simplifies rolling back
+     * extensive deletions.
+     */
+    Node *repr;
+
+    struct IteratorStrategy {
+        static Event const *next(Event const *action) {
+            return action->next;
+        }
+    };
+
+    typedef Inkscape::Util::ForwardPointerIterator<Event, IteratorStrategy> Iterator;
+    typedef Inkscape::Util::ForwardPointerIterator<Event const, IteratorStrategy> ConstIterator;
+
+    /**
+     * @brief If possible, combine this event with the next to reduce memory use
+     * @return Pointer to the optimized event chain, which may have changed
+     */
+    Event *optimizeOne() { return _optimizeOne(); }
+    /**
+     * @brief Undo this event to an observer
+     *
+     * This method notifies the specified observer of an action opposite to the one that
+     * is described by this event.
+     */
+    void undoOne(NodeObserver &observer) const {
+        _undoOne(observer);
+    }
+    /**
+     * @brief Replay this event to an observer
+     *
+     * This method notifies the specified event of the same action that it describes.
+     */
+    void replayOne(NodeObserver &observer) const {
+        _replayOne(observer);
+    }
+
+protected:
+    Event(Node *r, Event *n)
+    : next(n), serial(_next_serial++), repr(r) {}
+
+    virtual Event *_optimizeOne()=0;
+    virtual void _undoOne(NodeObserver &) const=0;
+    virtual void _replayOne(NodeObserver &) const=0;
+
+private:
+    static int _next_serial;
+};
+
+/**
+ * @brief Object representing child addition
+ */
+class EventAdd : public Event {
+public:
+    EventAdd(Node *repr, Node *c, Node *rr, Event *next)
+    : Event(repr, next), child(c), ref(rr) {}
+
+    /// The added child node
+    Node *child;
+    /// The node after which the child has been added, or NULL if it was added as first
+    Node *ref;
+
+private:
+    Event *_optimizeOne() override;
+    void _undoOne(NodeObserver &observer) const override;
+    void _replayOne(NodeObserver &observer) const override;
+};
+
+/**
+ * @brief Object representing child removal
+ */
+class EventDel : public Event {
+public:
+    EventDel(Node *repr, Node *c, Node *rr, Event *next)
+    : Event(repr, next), child(c), ref(rr) {}
+
+    /// The child node that was removed
+    Node *child;
+    /// The node after which the removed node was in the sibling order, or NULL if it was first
+    Node *ref;
+
+private:
+    Event *_optimizeOne() override;
+    void _undoOne(NodeObserver &observer) const override;
+    void _replayOne(NodeObserver &observer) const override;
+};
+
+/**
+ * @brief Object representing attribute change
+ */
+class EventChgAttr : public Event {
+public:
+    EventChgAttr(Node *repr, GQuark k,
+                 Inkscape::Util::ptr_shared ov,
+                 Inkscape::Util::ptr_shared nv,
+                 Event *next)
+    : Event(repr, next), key(k),
+      oldval(ov), newval(nv) {}
+
+    /// GQuark corresponding to the changed attribute's name
+    GQuark key;
+    /// Value of the attribute before the change
+    Inkscape::Util::ptr_shared oldval;
+    /// Value of the attribute after the change
+    Inkscape::Util::ptr_shared newval;
+
+private:
+    Event *_optimizeOne() override;
+    void _undoOne(NodeObserver &observer) const override;
+    void _replayOne(NodeObserver &observer) const override;
+};
+
+/**
+ * @brief Object representing content change
+ */
+class EventChgContent : public Event {
+public:
+    EventChgContent(Node *repr,
+                    Inkscape::Util::ptr_shared ov,
+                    Inkscape::Util::ptr_shared nv,
+                    Event *next)
+    : Event(repr, next), oldval(ov), newval(nv) {}
+
+    /// Content of the node before the change
+    Inkscape::Util::ptr_shared oldval;
+    /// Content of the node after the change
+    Inkscape::Util::ptr_shared newval;
+
+private:
+    Event *_optimizeOne() override;
+    void _undoOne(NodeObserver &observer) const override;
+    void _replayOne(NodeObserver &observer) const override;
+};
+
+/**
+ * @brief Object representing child order change
+ */
+class EventChgOrder : public Event {
+public:
+    EventChgOrder(Node *repr, Node *c, Node *orr, Node *nrr, Event *next)
+    : Event(repr, next), child(c),
+      oldref(orr), newref(nrr) {}
+
+    /// The node that was relocated in sibling order
+    Node *child;
+    /// The node after which the relocated node was in the sibling order before the change, or NULL if it was first
+    Node *oldref;
+    /// The node after which the relocated node is after the change, or if it's first
+    Node *newref;
+
+private:
+    Event *_optimizeOne() override;
+    void _undoOne(NodeObserver &observer) const override;
+    void _replayOne(NodeObserver &observer) const override;
+};
+
+/**
+ * @brief Object representing element name change.
+ */
+class EventChgElementName : public Event {
+public:
+    EventChgElementName(Node* repr, GQuark old_name, GQuark new_name, Event* next)
+        : Event(repr, next), old_name(old_name), new_name(new_name) {}
+
+    /// GQuark corresponding to the old element name.
+    GQuark old_name;
+    /// GQuark corresponding to the new element name.
+    GQuark new_name;
+
+private:
+    Event* _optimizeOne() override;
+    void _undoOne(NodeObserver& observer) const override;
+    void _replayOne(NodeObserver& observer) const override;
+};
+
+}
+}
+
+#endif
+/*
+  Local Variables:
+  mode:c++
+  c-file-style:"stroustrup"
+  c-file-offsets:((innamespace . 0)(inline-open . 0)(case-label . +))
+  indent-tabs-mode:nil
+  fill-column:99
+  End:
+*/
+// vim: filetype=cpp:expandtab:shiftwidth=4:tabstop=8:softtabstop=4:fileencoding=utf-8:textwidth=99 :