diff --git a/Source/DotNET/Engine.Specs/for_FreeformSlotArrangementEvaluator/when_evaluating_against_the_shared_fixture_corpus.cs b/Source/DotNET/Engine.Specs/for_FreeformSlotArrangementEvaluator/when_evaluating_against_the_shared_fixture_corpus.cs
new file mode 100644
index 0000000..110ef78
--- /dev/null
+++ b/Source/DotNET/Engine.Specs/for_FreeformSlotArrangementEvaluator/when_evaluating_against_the_shared_fixture_corpus.cs
@@ -0,0 +1,72 @@
+// Copyright (c) Cratis. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using System.Text.Json;
+using Cratis.Scene.Engine.Layouts;
+using Cratis.Scene.Model.Layouts;
+using Cratis.Scene.Model.SizeClasses;
+
+namespace Cratis.Scene.Engine.for_FreeformSlotArrangementEvaluator;
+
+public class when_evaluating_against_the_shared_fixture_corpus : Specification
+{
+    record FixtureCase(string Name, FreeformSlotArrangement Arrangement, SizeClass SizeClass, string? ExpectedTag);
+
+    List<FixtureCase> _cases = null!;
+    List<(FixtureCase Case, string? ActualTag)> _results = null!;
+
+    void Establish()
+    {
+        var manifestPath = Path.Combine(FindRepositoryRoot(), "layout-evaluation-fixtures.json");
+        using var document = JsonDocument.Parse(File.ReadAllText(manifestPath));
+
+        _cases = document.RootElement.GetProperty("freeformCases").EnumerateArray().Select(ToFixtureCase).ToList();
+    }
+
+    void Because() => _results = [.. _cases.Select(fixtureCase => (fixtureCase, TagOf(FreeformSlotArrangementEvaluator.Evaluate(fixtureCase.Arrangement, fixtureCase.SizeClass))))];
+
+    [Fact]
+    void should_match_the_expected_tag_for_every_case()
+    {
+        foreach (var (fixtureCase, actualTag) in _results)
+        {
+            (fixtureCase.Name, actualTag).ShouldEqual((fixtureCase.Name, fixtureCase.ExpectedTag));
+        }
+    }
+
+    static FixtureCase ToFixtureCase(JsonElement element)
+    {
+        var name = element.GetProperty("name").GetString()!;
+
+        var variants = element.GetProperty("variants").EnumerateArray()
+            .Select(variantElement => new FreeformSlotVariant(
+                new SizeClass(
+                    Enum.Parse<WidthSizeClass>(variantElement.GetProperty("width").GetString()!),
+                    Enum.Parse<HeightSizeClass>(variantElement.GetProperty("height").GetString()!)),
+                [new SlotPlacement(variantElement.GetProperty("tag").GetString()!, 0, 0, 0, 0)]))
+            .ToList();
+
+        var sizeClassElement = element.GetProperty("sizeClass");
+        var sizeClass = new SizeClass(
+            Enum.Parse<WidthSizeClass>(sizeClassElement.GetProperty("width").GetString()!),
+            Enum.Parse<HeightSizeClass>(sizeClassElement.GetProperty("height").GetString()!));
+
+        var expectedTagElement = element.GetProperty("expectedTag");
+        var expectedTag = expectedTagElement.ValueKind == JsonValueKind.Null ? null : expectedTagElement.GetString();
+
+        return new(name, new FreeformSlotArrangement(variants), sizeClass, expectedTag);
+    }
+
+    static string? TagOf(FreeformSlotVariant? variant) => variant?.Placements.Single().SlotName;
+
+    static string FindRepositoryRoot()
+    {
+        var directory = new DirectoryInfo(AppContext.BaseDirectory);
+        while (directory is not null && !File.Exists(Path.Combine(directory.FullName, "Scene.slnx")))
+        {
+            directory = directory.Parent;
+        }
+
+        return directory?.FullName ?? throw new DirectoryNotFoundException("Could not locate the repository root (Scene.slnx) above " + AppContext.BaseDirectory);
+    }
+}
diff --git a/Source/DotNET/Engine/Layouts/FreeformSlotArrangementEvaluator.cs b/Source/DotNET/Engine/Layouts/FreeformSlotArrangementEvaluator.cs
new file mode 100644
index 0000000..8c37cab
--- /dev/null
+++ b/Source/DotNET/Engine/Layouts/FreeformSlotArrangementEvaluator.cs
@@ -0,0 +1,29 @@
+// Copyright (c) Cratis. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using Cratis.Scene.Model.Layouts;
+using Cratis.Scene.Model.SizeClasses;
+
+namespace Cratis.Scene.Engine.Layouts;
+
+/// <summary>
+/// Evaluates a <see cref="FreeformSlotArrangement"/> for a given <see cref="SizeClass"/> - the counterpart
+/// to <see cref="FreeformArrangementEvaluator"/> for a <see cref="Layout"/>'s own macro
+/// <see cref="Layout.Arrangement"/>, which places the layout's slots themselves rather than the content of
+/// one slot.
+/// </summary>
+public static class FreeformSlotArrangementEvaluator
+{
+    /// <summary>
+    /// Selects the <see cref="FreeformSlotVariant"/> that targets a given <see cref="SizeClass"/>.
+    /// </summary>
+    /// <param name="arrangement">The <see cref="FreeformSlotArrangement"/> to evaluate.</param>
+    /// <param name="sizeClass">The current <see cref="SizeClass"/>.</param>
+    /// <returns>
+    /// The variant whose <see cref="FreeformSlotVariant.SizeClass"/> exactly matches, or <see langword="null"/>
+    /// when nothing targets it. There is deliberately no fallback here - a size class with no matching
+    /// variant is a design-time/build-time warning elsewhere, never a silently picked variant.
+    /// </returns>
+    public static FreeformSlotVariant? Evaluate(FreeformSlotArrangement arrangement, SizeClass sizeClass) =>
+        arrangement.Variants.FirstOrDefault(variant => variant.SizeClass == sizeClass);
+}
diff --git a/Source/DotNET/Model/Layouts/Arrangement.cs b/Source/DotNET/Model/Layouts/Arrangement.cs
index 1c7f478..2bfb068 100644
--- a/Source/DotNET/Model/Layouts/Arrangement.cs
+++ b/Source/DotNET/Model/Layouts/Arrangement.cs
@@ -4,7 +4,12 @@
 namespace Cratis.Scene.Model.Layouts;
 
 /// <summary>
-/// How a <see cref="Slot"/>'s content is arranged: <see cref="FlowArrangement"/> (reflowing, computed per
-/// size class) or <see cref="FreeformArrangement"/> (one placement variant per size class).
+/// How content is arranged: <see cref="FlowArrangement"/> (reflowing, computed per size class) or
+/// <see cref="FreeformArrangement"/>/<see cref="FreeformSlotArrangement"/> (one placement variant per size
+/// class). Used at two levels - a <see cref="Layout"/>'s own <see cref="Layout.Arrangement"/> positions its
+/// named <see cref="Slot"/>s relative to each other (leaves reference a slot by name: <see cref="FlowSlotLeaf"/>/
+/// <see cref="SlotPlacement"/>), while a <see cref="Slot"/>'s own <see cref="Slot.Arrangement"/> positions
+/// that slot's own filled content elements (leaves carry the element itself: <see cref="FlowLeaf"/>/
+/// <see cref="ElementPlacement"/>).
 /// </summary>
 public abstract record Arrangement;
diff --git a/Source/DotNET/Model/Layouts/FlowSlotLeaf.cs b/Source/DotNET/Model/Layouts/FlowSlotLeaf.cs
new file mode 100644
index 0000000..4c2dc68
--- /dev/null
+++ b/Source/DotNET/Model/Layouts/FlowSlotLeaf.cs
@@ -0,0 +1,12 @@
+// Copyright (c) Cratis. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+namespace Cratis.Scene.Model.Layouts;
+
+/// <summary>
+/// A <see cref="FlowNode"/> leaf that positions one of a <see cref="Layout"/>'s own named <see cref="Slot"/>s
+/// within its macro <see cref="Layout.Arrangement"/> tree - the counterpart to <see cref="FlowLeaf"/>, which
+/// positions an element within a single slot's own content instead of positioning a slot within the layout.
+/// </summary>
+/// <param name="SlotName">The name of the <see cref="Slot"/> being positioned.</param>
+public record FlowSlotLeaf(string SlotName) : FlowNode;
diff --git a/Source/DotNET/Model/Layouts/FreeformSlotArrangement.cs b/Source/DotNET/Model/Layouts/FreeformSlotArrangement.cs
new file mode 100644
index 0000000..3a60b6a
--- /dev/null
+++ b/Source/DotNET/Model/Layouts/FreeformSlotArrangement.cs
@@ -0,0 +1,13 @@
+// Copyright (c) Cratis. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+namespace Cratis.Scene.Model.Layouts;
+
+/// <summary>
+/// Arranges a <see cref="Layout"/>'s own named <see cref="Slot"/>s with one placement variant per size
+/// class - the Xcode-storyboard model applied to the layout's slots themselves, rather than to the content
+/// of one slot (see <see cref="FreeformArrangement"/>). The same slot set is shared across every variant;
+/// only placement differs.
+/// </summary>
+/// <param name="Variants">The placement variants, one per targeted size class.</param>
+public record FreeformSlotArrangement(IReadOnlyList<FreeformSlotVariant> Variants) : Arrangement;
diff --git a/Source/DotNET/Model/Layouts/FreeformSlotVariant.cs b/Source/DotNET/Model/Layouts/FreeformSlotVariant.cs
new file mode 100644
index 0000000..c33eb30
--- /dev/null
+++ b/Source/DotNET/Model/Layouts/FreeformSlotVariant.cs
@@ -0,0 +1,16 @@
+// Copyright (c) Cratis. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+using Cratis.Scene.Model.SizeClasses;
+
+namespace Cratis.Scene.Model.Layouts;
+
+/// <summary>
+/// One placement variant of a <see cref="FreeformSlotArrangement"/>, targeting a specific size class - the
+/// counterpart to <see cref="FreeformVariant"/>, which places elements within a single slot instead of
+/// placing a layout's own slots. A size class with no matching variant is a compiler/engine warning, never
+/// a silent fallback, matching <see cref="FreeformVariant"/>.
+/// </summary>
+/// <param name="SizeClass">The size class this variant targets.</param>
+/// <param name="Placements">Where each of the layout's slots is placed for this variant.</param>
+public record FreeformSlotVariant(SizeClass SizeClass, IReadOnlyList<SlotPlacement> Placements);
diff --git a/Source/DotNET/Model/Layouts/Layout.cs b/Source/DotNET/Model/Layouts/Layout.cs
index 781c342..ad44a57 100644
--- a/Source/DotNET/Model/Layouts/Layout.cs
+++ b/Source/DotNET/Model/Layouts/Layout.cs
@@ -10,4 +10,11 @@ namespace Cratis.Scene.Model.Layouts;
 /// </summary>
 /// <param name="Name">The layout's name.</param>
 /// <param name="Slots">The slots the layout declares, in declaration order.</param>
-public record Layout(string Name, IReadOnlyList<Slot> Slots);
+/// <param name="Arrangement">
+/// How the layout's own <paramref name="Slots"/> position relative to each other - a <see cref="FlowArrangement"/>
+/// (leaves are <see cref="FlowSlotLeaf"/>) or <see cref="FreeformSlotArrangement"/>, or <see langword="null"/>
+/// for the slots' declaration order with no further positioning information. Distinct from each
+/// <see cref="Layouts.Slot"/>'s own <see cref="Slot.Arrangement"/>, which positions that one slot's filled
+/// content instead of positioning the slots themselves.
+/// </param>
+public record Layout(string Name, IReadOnlyList<Slot> Slots, Arrangement? Arrangement = null);
diff --git a/Source/DotNET/Model/Layouts/SlotPlacement.cs b/Source/DotNET/Model/Layouts/SlotPlacement.cs
new file mode 100644
index 0000000..295691d
--- /dev/null
+++ b/Source/DotNET/Model/Layouts/SlotPlacement.cs
@@ -0,0 +1,16 @@
+// Copyright (c) Cratis. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+namespace Cratis.Scene.Model.Layouts;
+
+/// <summary>
+/// The absolute position and size of one of a <see cref="Layout"/>'s own named <see cref="Slot"/>s within a
+/// <see cref="FreeformSlotVariant"/> - the counterpart to <see cref="ElementPlacement"/>, which places an
+/// element within a single slot's own content instead of placing a slot within the layout.
+/// </summary>
+/// <param name="SlotName">The name of the <see cref="Slot"/> being placed.</param>
+/// <param name="X">The horizontal offset.</param>
+/// <param name="Y">The vertical offset.</param>
+/// <param name="Width">The width.</param>
+/// <param name="Height">The height.</param>
+public record SlotPlacement(string SlotName, double X, double Y, double Width, double Height);
diff --git a/Source/JavaScript/engine/evaluateFreeformSlotArrangement.ts b/Source/JavaScript/engine/evaluateFreeformSlotArrangement.ts
new file mode 100644
index 0000000..8b2ddaf
--- /dev/null
+++ b/Source/JavaScript/engine/evaluateFreeformSlotArrangement.ts
@@ -0,0 +1,17 @@
+// Copyright (c) Cratis. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+import { FreeformSlotArrangement, FreeformSlotVariant, SizeClass } from '@cratis/scene.model';
+
+/**
+ * Selects the {@link FreeformSlotVariant} that targets a given {@link SizeClass} - the counterpart to
+ * {@link evaluateFreeformArrangement} for a `Layout`'s own macro `arrangement`, which places the layout's
+ * slots themselves rather than the content of one slot.
+ *
+ * @param arrangement The {@link FreeformSlotArrangement} to evaluate.
+ * @param sizeClass The current {@link SizeClass}.
+ * @returns The variant whose size class exactly matches, or `undefined` when nothing targets it. There is deliberately no fallback here - a size class with no matching variant is a design-time/build-time warning elsewhere, never a silently picked variant.
+ */
+export function evaluateFreeformSlotArrangement(arrangement: FreeformSlotArrangement, sizeClass: SizeClass): FreeformSlotVariant | undefined {
+    return arrangement.variants.find(variant => variant.sizeClass.width === sizeClass.width && variant.sizeClass.height === sizeClass.height);
+}
diff --git a/Source/JavaScript/engine/for_evaluateFreeformSlotArrangement/when_evaluating_against_the_shared_fixture_corpus.ts b/Source/JavaScript/engine/for_evaluateFreeformSlotArrangement/when_evaluating_against_the_shared_fixture_corpus.ts
new file mode 100644
index 0000000..ea8ab02
--- /dev/null
+++ b/Source/JavaScript/engine/for_evaluateFreeformSlotArrangement/when_evaluating_against_the_shared_fixture_corpus.ts
@@ -0,0 +1,47 @@
+// Copyright (c) Cratis. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+import { readFileSync } from 'node:fs';
+import { join } from 'node:path';
+import { FreeformSlotArrangement, HeightSizeClass, SizeClass, WidthSizeClass } from '@cratis/scene.model';
+import { evaluateFreeformSlotArrangement } from '../index';
+
+interface FixtureVariant {
+    width: WidthSizeClass;
+    height: HeightSizeClass;
+    tag: string;
+}
+
+interface FixtureCase {
+    name: string;
+    variants: FixtureVariant[];
+    sizeClass: SizeClass;
+    expectedTag: string | null;
+}
+
+interface FixtureCorpus {
+    freeformCases: FixtureCase[];
+}
+
+const manifestPath = join(import.meta.dirname, '..', '..', '..', '..', 'layout-evaluation-fixtures.json');
+const corpus = JSON.parse(readFileSync(manifestPath, 'utf-8')) as FixtureCorpus;
+
+describe('when evaluating against the shared fixture corpus', () => {
+    for (const fixtureCase of corpus.freeformCases) {
+        it(`should match the expected tag for "${fixtureCase.name}"`, () => {
+            const arrangement: FreeformSlotArrangement = {
+                variants: fixtureCase.variants.map(variant => ({
+                    sizeClass: { width: variant.width, height: variant.height },
+                    placements: [{ slotName: variant.tag, x: 0, y: 0, width: 0, height: 0 }],
+                })),
+            };
+
+            const result = evaluateFreeformSlotArrangement(arrangement, fixtureCase.sizeClass);
+            if (fixtureCase.expectedTag === null) {
+                (result === undefined).should.be.true;
+            } else {
+                result!.placements[0].slotName.should.equal(fixtureCase.expectedTag);
+            }
+        });
+    }
+});
diff --git a/Source/JavaScript/engine/index.ts b/Source/JavaScript/engine/index.ts
index 0add27c..11e19be 100644
--- a/Source/JavaScript/engine/index.ts
+++ b/Source/JavaScript/engine/index.ts
@@ -10,6 +10,7 @@ export * from './resolveComponentName';
 export * from './computeSizeClass';
 export * from './evaluateFlowArrangement';
 export * from './evaluateFreeformArrangement';
+export * from './evaluateFreeformSlotArrangement';
 export * from './aggregateContributions';
 export * from './themeCompatibility';
 export * from './buildStarterProfile';
diff --git a/Source/JavaScript/model/layouts/Arrangement.ts b/Source/JavaScript/model/layouts/Arrangement.ts
index abd8352..ebd71f8 100644
--- a/Source/JavaScript/model/layouts/Arrangement.ts
+++ b/Source/JavaScript/model/layouts/Arrangement.ts
@@ -2,7 +2,11 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
 /**
- * How a {@link Slot}'s content is arranged: {@link FlowArrangement} (reflowing, computed per size class)
- * or {@link FreeformArrangement} (one placement variant per size class).
+ * How content is arranged: {@link FlowArrangement} (reflowing, computed per size class) or
+ * {@link FreeformArrangement}/{@link FreeformSlotArrangement} (one placement variant per size class). Used
+ * at two levels - a {@link Layout}'s own `arrangement` positions its named {@link Slot}s relative to each
+ * other (leaves reference a slot by name: {@link FlowSlotLeaf}/{@link SlotPlacement}), while a
+ * {@link Slot}'s own `arrangement` positions that slot's own filled content elements (leaves carry the
+ * element itself: {@link FlowLeaf}/{@link ElementPlacement}).
  */
 export interface Arrangement {}
diff --git a/Source/JavaScript/model/layouts/FlowSlotLeaf.ts b/Source/JavaScript/model/layouts/FlowSlotLeaf.ts
new file mode 100644
index 0000000..3c8bcae
--- /dev/null
+++ b/Source/JavaScript/model/layouts/FlowSlotLeaf.ts
@@ -0,0 +1,15 @@
+// Copyright (c) Cratis. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+import { FlowNode } from './FlowNode';
+
+/**
+ * A {@link FlowNode} leaf that positions one of a {@link Layout}'s own named {@link Slot}s within its
+ * macro `arrangement` tree - the counterpart to {@link FlowLeaf}, which positions an element within a
+ * single slot's own content instead of positioning a slot within the layout.
+ */
+export interface FlowSlotLeaf extends FlowNode {
+    slotName: string;
+}
+
+export const FlowSlotLeafPropertyNames: (keyof FlowSlotLeaf)[] = ['slotName'];
diff --git a/Source/JavaScript/model/layouts/FreeformSlotArrangement.ts b/Source/JavaScript/model/layouts/FreeformSlotArrangement.ts
new file mode 100644
index 0000000..f515c29
--- /dev/null
+++ b/Source/JavaScript/model/layouts/FreeformSlotArrangement.ts
@@ -0,0 +1,17 @@
+// Copyright (c) Cratis. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+import { Arrangement } from './Arrangement';
+import { FreeformSlotVariant } from './FreeformSlotVariant';
+
+/**
+ * Arranges a {@link Layout}'s own named {@link Slot}s with one placement variant per size class - the
+ * Xcode-storyboard model applied to the layout's slots themselves, rather than to the content of one slot
+ * (see {@link FreeformArrangement}). The same slot set is shared across every variant; only placement
+ * differs.
+ */
+export interface FreeformSlotArrangement extends Arrangement {
+    variants: FreeformSlotVariant[];
+}
+
+export const FreeformSlotArrangementPropertyNames: (keyof FreeformSlotArrangement)[] = ['variants'];
diff --git a/Source/JavaScript/model/layouts/FreeformSlotVariant.ts b/Source/JavaScript/model/layouts/FreeformSlotVariant.ts
new file mode 100644
index 0000000..79d03db
--- /dev/null
+++ b/Source/JavaScript/model/layouts/FreeformSlotVariant.ts
@@ -0,0 +1,18 @@
+// Copyright (c) Cratis. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+import { SizeClass } from '../sizeClasses';
+import { SlotPlacement } from './SlotPlacement';
+
+/**
+ * One placement variant of a {@link FreeformSlotArrangement}, targeting a specific size class - the
+ * counterpart to {@link FreeformVariant}, which places elements within a single slot instead of placing a
+ * layout's own slots. A size class with no matching variant is a compiler/engine warning, never a silent
+ * fallback, matching {@link FreeformVariant}.
+ */
+export interface FreeformSlotVariant {
+    sizeClass: SizeClass;
+    placements: SlotPlacement[];
+}
+
+export const FreeformSlotVariantPropertyNames: (keyof FreeformSlotVariant)[] = ['sizeClass', 'placements'];
diff --git a/Source/JavaScript/model/layouts/Layout.ts b/Source/JavaScript/model/layouts/Layout.ts
index 1d8dae6..409e0c1 100644
--- a/Source/JavaScript/model/layouts/Layout.ts
+++ b/Source/JavaScript/model/layouts/Layout.ts
@@ -1,6 +1,7 @@
 // Copyright (c) Cratis. All rights reserved.
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 
+import { Arrangement } from './Arrangement';
 import { Slot } from './Slot';
 
 /**
@@ -11,6 +12,15 @@ import { Slot } from './Slot';
 export interface Layout {
     name: string;
     slots: Slot[];
+
+    /**
+     * How the layout's own `slots` position relative to each other - a {@link FlowArrangement} (leaves
+     * are {@link FlowSlotLeaf}) or {@link FreeformSlotArrangement}, or `undefined` for the slots'
+     * declaration order with no further positioning information. Distinct from each {@link Slot}'s own
+     * `arrangement`, which positions that one slot's filled content instead of positioning the slots
+     * themselves.
+     */
+    arrangement?: Arrangement;
 }
 
-export const LayoutPropertyNames: (keyof Layout)[] = ['name', 'slots'];
+export const LayoutPropertyNames: (keyof Layout)[] = ['name', 'slots', 'arrangement'];
diff --git a/Source/JavaScript/model/layouts/SlotPlacement.ts b/Source/JavaScript/model/layouts/SlotPlacement.ts
new file mode 100644
index 0000000..c04e88e
--- /dev/null
+++ b/Source/JavaScript/model/layouts/SlotPlacement.ts
@@ -0,0 +1,17 @@
+// Copyright (c) Cratis. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+
+/**
+ * The absolute position and size of one of a {@link Layout}'s own named {@link Slot}s within a
+ * {@link FreeformSlotVariant} - the counterpart to {@link ElementPlacement}, which places an element
+ * within a single slot's own content instead of placing a slot within the layout.
+ */
+export interface SlotPlacement {
+    slotName: string;
+    x: number;
+    y: number;
+    width: number;
+    height: number;
+}
+
+export const SlotPlacementPropertyNames: (keyof SlotPlacement)[] = ['slotName', 'x', 'y', 'width', 'height'];
diff --git a/Source/JavaScript/model/layouts/index.ts b/Source/JavaScript/model/layouts/index.ts
index 911f55c..206308f 100644
--- a/Source/JavaScript/model/layouts/index.ts
+++ b/Source/JavaScript/model/layouts/index.ts
@@ -12,6 +12,10 @@ export * from './FlowRow';
 export * from './FlowColumn';
 export * from './FlowGrid';
 export * from './FlowLeaf';
+export * from './FlowSlotLeaf';
 export * from './FreeformArrangement';
 export * from './FreeformVariant';
 export * from './ElementPlacement';
+export * from './FreeformSlotArrangement';
+export * from './FreeformSlotVariant';
+export * from './SlotPlacement';
diff --git a/layout-evaluation-fixtures.json b/layout-evaluation-fixtures.json
index 8477a34..cd0d338 100644
--- a/layout-evaluation-fixtures.json
+++ b/layout-evaluation-fixtures.json
@@ -1,5 +1,5 @@
 {
-    "description": "Shared behavior corpus for Cratis.Scene.Engine.Layouts.FlowArrangementEvaluator/FreeformArrangementEvaluator (C#) and evaluateFlowArrangement/evaluateFreeformArrangement (TypeScript, @cratis/scene.engine) - both sides assert every case here independently, so the two implementations of Cratis/Scene#4's selection algorithm cannot drift apart. Trees and placements are reduced to a distinguishing 'tag' string, since the evaluators only select which one wins - they never descend into or transform the tree itself.",
+    "description": "Shared behavior corpus for Cratis.Scene.Engine.Layouts.FlowArrangementEvaluator/FreeformArrangementEvaluator (C#) and evaluateFlowArrangement/evaluateFreeformArrangement (TypeScript, @cratis/scene.engine) - both sides assert every case here independently, so the two implementations of Cratis/Scene#4's selection algorithm cannot drift apart. Trees and placements are reduced to a distinguishing 'tag' string, since the evaluators only select which one wins - they never descend into or transform the tree itself. 'freeformCases' is reused verbatim (the 'tag' read as a slot name instead of an element id) by FreeformSlotArrangementEvaluator/evaluateFreeformSlotArrangement - the slot-vs-element leaf content is exactly what those evaluators don't look at, so one corpus proves both.",
     "flowCases": [
         {
             "name": "no overrides - the base root always wins",
diff --git a/scene-model-shape.json b/scene-model-shape.json
index 9fc6017..e69ebc5 100644
--- a/scene-model-shape.json
+++ b/scene-model-shape.json
@@ -14,7 +14,7 @@
         "ItemsControl": ["itemsSource", "itemTemplate"],
         "ContentControl": ["content"],
         "ExternalComponent": ["componentName", "slots"],
-        "Layout": ["name", "slots"],
+        "Layout": ["name", "slots", "arrangement"],
         "Slot": ["name", "arrangement"],
         "Arrangement": [],
         "FlowArrangement": ["root", "overrides"],
@@ -25,9 +25,13 @@
         "FlowColumn": [],
         "FlowGrid": ["columns", "rows"],
         "FlowLeaf": ["content"],
+        "FlowSlotLeaf": ["slotName"],
         "FreeformArrangement": ["variants"],
         "FreeformVariant": ["sizeClass", "placements"],
         "ElementPlacement": ["element", "x", "y", "width", "height"],
+        "FreeformSlotArrangement": ["variants"],
+        "FreeformSlotVariant": ["sizeClass", "placements"],
+        "SlotPlacement": ["slotName", "x", "y", "width", "height"],
         "PopulateSource": [],
         "PopulateViaQuery": ["queryName", "parameterBindings"],
         "PopulateFromItem": ["itemBinding"],