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diff --git a/src/Text/Def/TextUI/MultiCaret/ISelectionTransformer.cs b/src/Text/Def/TextUI/MultiCaret/ISelectionTransformer.cs
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+++ b/src/Text/Def/TextUI/MultiCaret/ISelectionTransformer.cs
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+//
+//  Copyright (c) Microsoft Corporation. All rights reserved.
+//  Licensed under the MIT License. See License.txt in the project root for license information.
+//
+namespace Microsoft.VisualStudio.Text
+{
+    /// <summary>
+    /// Allows changing existing <see cref="ISelection"/> objects as part of <see cref="IMultiSelectionBroker.PerformActionOnAllSelections(System.Action{ISelectionTransformer})"
+    /// and <see cref="IMultiSelectionBroker.TryPerformActionOnRegion(ISelection, out ISelection, System.Action{ISelectionTransformer})"/>./>
+    /// </summary>
+    public interface ISelectionTransformer
+    {
+        /// <summary>
+        /// Gets the Selection to transform. This will change through calls to <see cref="PerformAction(PredefinedSelectionTransformations)"/>,
+        /// <see cref="MoveTo(VirtualSnapshotPoint, bool, PositionAffinity)"/>, and
+        /// <see cref="MoveTo(VirtualSnapshotPoint, VirtualSnapshotPoint, VirtualSnapshotPoint, PositionAffinity)"/>.
+        /// </summary>
+        Selection Selection { get; }
+
+        /// <summary>
+        /// Moves the insertion and active points to the given location.
+        /// </summary>
+        /// <param name="point">The point to move to.</param>
+        /// <param name="select">If <c>true</c>, leaves the anchor point where it is. If <c>false</c>, moves the anchor point too.</param>
+        /// <param name="insertionPointAffinity">
+        /// The affinity of the insertion point. This is used in places like word-wrap where one buffer position can represent both the
+        /// end of one line and the beginning of the next.
+        /// </param>
+        void MoveTo(VirtualSnapshotPoint point, bool select, PositionAffinity insertionPointAffinity);
+
+        /// <summary>
+        /// Sets the anchor, active, and insertion points to the specified locations.
+        /// </summary>
+        /// <param name="anchorPoint">Specifies the stationary end of the selection span.</param>
+        /// <param name="activePoint">Specifies the mobile end of the selection span.</param>
+        /// <param name="insertionPoint">Specifies the location of the caret.</param>
+        /// <param name="insertionPointAffinity">
+        /// Specifies the affinity of the insertion point. This is used in places like word-wrap where one buffer position can represent both the
+        /// end of one line and the beginning of the next.
+        /// </param>
+        void MoveTo(VirtualSnapshotPoint anchorPoint, VirtualSnapshotPoint activePoint, VirtualSnapshotPoint insertionPoint, PositionAffinity insertionPointAffinity);
+
+        /// <summary>
+        /// Updates internal state to cache the current location as the desired reference point for navigation events.
+        /// </summary>
+        /// <remarks>
+        /// This affects events like <see cref="PredefinedSelectionTransformations.MoveToPreviousLine"/> where the current
+        /// X location of the rendered caret is used to project to the new location. Typically this method should be called
+        /// in cases where the user is stating where they want to focus. Since this grabs the current state, there is no
+        /// equivalent release method.
+        /// </remarks>
+        void CapturePreferredReferencePoint();
+
+        /// <summary>
+        /// Updates internal state to cache the current x location as the desired reference point for navigation events.
+        /// </summary>
+        /// <remarks>
+        /// This affects events like <see cref="PredefinedSelectionTransformations.MoveToPreviousLine"/> where the current
+        /// X location of the rendered caret is used to project to the new location. Typically this method should be called
+        /// in cases where the user is stating where they want to focus. Since this grabs the current state, there is no
+        /// equivalent release method.
+        /// </remarks>
+        void CapturePreferredXReferencePoint();
+
+        /// <summary>
+        /// Updates internal state to cache the current y location as the desired reference point for navigation events.
+        /// </summary>
+        /// <remarks>
+        /// This affects events like <see cref="PredefinedSelectionTransformations.MovePageUp"/> where the current
+        /// Y location of the rendered caret is used to project to the new location. Typically this method should be called
+        /// in cases where the user is stating where they want to focus. Since this grabs the current state, there is no
+        /// equivalent release method.
+        /// </remarks>
+        void CapturePreferredYReferencePoint();
+
+        /// <summary>
+        /// Transforms <see cref="Selection"/> in a predefined way.
+        /// </summary>
+        /// <param name="action">The kind of transformation to perform</param>
+        void PerformAction(PredefinedSelectionTransformations action);
+    }
+}