diff --git a/src/json-crdt-extensions/constants.ts b/src/json-crdt-extensions/constants.ts
index fd071bca51..2364d76b94 100644
--- a/src/json-crdt-extensions/constants.ts
+++ b/src/json-crdt-extensions/constants.ts
@@ -4,7 +4,3 @@ export const enum ExtensionId {
   peritext = 2,
   quill = 3,
 }
-
-export const enum Chars {
-  BlockSplitSentinel = '\n',
-}
diff --git a/src/json-crdt-extensions/peritext/Peritext.ts b/src/json-crdt-extensions/peritext/Peritext.ts
index aa31a19424..7b5b56778f 100644
--- a/src/json-crdt-extensions/peritext/Peritext.ts
+++ b/src/json-crdt-extensions/peritext/Peritext.ts
@@ -1,14 +1,18 @@
+import {printTree} from 'sonic-forest/lib/print/printTree';
 import {Anchor} from './rga/constants';
 import {Point} from './rga/Point';
 import {Range} from './rga/Range';
 import {Editor} from './editor/Editor';
-import {printTree} from '../../util/print/printTree';
 import {ArrNode, StrNode} from '../../json-crdt/nodes';
 import {Slices} from './slice/Slices';
-import {type ITimestampStruct} from '../../json-crdt-patch/clock';
+import {Overlay} from './overlay/Overlay';
+import {Chars} from './constants';
+import type {ITimestampStruct} from '../../json-crdt-patch/clock';
 import type {Model} from '../../json-crdt/model';
 import type {Printable} from '../../util/print/types';
 import type {StringChunk} from './util/types';
+import type {SliceType} from './types';
+import type {MarkerSlice} from './slice/MarkerSlice';
 
 /**
  * Context for a Peritext instance. Contains all the data and methods needed to
@@ -17,6 +21,7 @@ import type {StringChunk} from './util/types';
 export class Peritext implements Printable {
   public readonly slices: Slices;
   public readonly editor: Editor;
+  public readonly overlay = new Overlay(this);
 
   constructor(
     public readonly model: Model,
@@ -43,6 +48,17 @@ export class Peritext implements Printable {
     return curr;
   }
 
+  /** Select a single character before a point. */
+  public findCharBefore(point: Point): Range | undefined {
+    if (point.anchor === Anchor.After) {
+      const chunk = point.chunk();
+      if (chunk && !chunk.del) return this.range(this.point(point.id, Anchor.Before), point);
+    }
+    const id = point.prevId();
+    if (!id) return;
+    return this.range(this.point(id, Anchor.Before), this.point(id, Anchor.After));
+  }
+
   // ------------------------------------------------------------------- points
 
   /**
@@ -159,15 +175,19 @@ export class Peritext implements Printable {
     return textId;
   }
 
-  /** Select a single character before a point. */
-  public findCharBefore(point: Point): Range | undefined {
-    if (point.anchor === Anchor.After) {
-      const chunk = point.chunk();
-      if (chunk && !chunk.del) return this.range(this.point(point.id, Anchor.Before), point);
-    }
-    const id = point.prevId();
-    if (!id) return;
-    return this.range(this.point(id, Anchor.Before), this.point(id, Anchor.After));
+  public insMarker(after: ITimestampStruct, type: SliceType, data?: unknown, char: string = Chars.BlockSplitSentinel): MarkerSlice {
+    const api = this.model.api;
+    const builder = api.builder;
+    const str = this.str;
+    /**
+     * We skip one clock cycle to prevent Block-wise RGA from merging adjacent
+     * characters. We want the marker chunk to always be its own distinct chunk.
+     */
+    builder.nop(1);
+    const textId = builder.insStr(str.id, after, char[0]);
+    const point = this.point(textId, Anchor.Before);
+    const range = this.range(point, point);
+    return this.slices.insMarker(range, type, data);
   }
 
   // ---------------------------------------------------------------- Printable
diff --git a/src/json-crdt-extensions/peritext/constants.ts b/src/json-crdt-extensions/peritext/constants.ts
new file mode 100644
index 0000000000..05532030bb
--- /dev/null
+++ b/src/json-crdt-extensions/peritext/constants.ts
@@ -0,0 +1,3 @@
+export const enum Chars {
+  BlockSplitSentinel = '\n',
+}
diff --git a/src/json-crdt-extensions/peritext/editor/Editor.ts b/src/json-crdt-extensions/peritext/editor/Editor.ts
index de975f2133..5f5f654d99 100644
--- a/src/json-crdt-extensions/peritext/editor/Editor.ts
+++ b/src/json-crdt-extensions/peritext/editor/Editor.ts
@@ -3,11 +3,13 @@ import {Anchor} from '../rga/constants';
 import {SliceBehavior} from '../slice/constants';
 import {tick, type ITimestampStruct} from '../../../json-crdt-patch/clock';
 import {PersistedSlice} from '../slice/PersistedSlice';
+import {Chars} from '../constants';
 import type {Range} from '../rga/Range';
 import type {Peritext} from '../Peritext';
 import type {Printable} from '../../../util/print/types';
 import type {Point} from '../rga/Point';
 import type {SliceType} from '../types';
+import type {MarkerSlice} from '../slice/MarkerSlice';
 
 export class Editor implements Printable {
   /**
@@ -132,4 +134,9 @@ export class Editor implements Printable {
   public insertEraseSlice(type: SliceType, data?: unknown | ITimestampStruct): PersistedSlice {
     return this.txt.slices.ins(this.cursor, SliceBehavior.Erase, type, data);
   }
+
+  public insMarker(type: SliceType, data?: unknown): MarkerSlice {
+    const after = this.collapseSelection();
+    return this.txt.insMarker(after, type, data, Chars.BlockSplitSentinel);
+  }
 }