diff --git a/docs/architecture/frames.md b/docs/architecture/frames.md
index 300af5d..d3d0b9e 100644
--- a/docs/architecture/frames.md
+++ b/docs/architecture/frames.md
@@ -16,8 +16,12 @@ path reads the live DOM. The **vector print path** (`export/pdf.ts`) handles it:
 `hoistTextBoxes` gives each box a paragraph of its own before serializing, and
 `buildBodyHtml` drops the two empty paragraphs the split then leaves around it — so the
 box prints as a block between whole paragraphs, which is how it printed as one.
-An **AutoText** entry holding a box keeps the box's text and loses the frame; so does a
-paste from another window.
+The **clipboard** handles it the other way: `boxClipboardSerializer` (a
+`clipboardSerializer` prop) writes each box as an inline `<span data-tbx>` carrying its
+blocks as JSON, and the `span[data-tbx]` parse rule's `getContent` reads them back — so a
+paste into another window keeps the box where it stood in the line, while a program that
+cannot read the attribute still gets the span's plain text. An **AutoText** entry stores
+the slice's nodes for the same reason (`storage/autoText.ts`).
 
 ## Clicking a float
 
diff --git a/src/lib/editor/extensions/textBox.ts b/src/lib/editor/extensions/textBox.ts
index 8fcdd56..f124670 100644
--- a/src/lib/editor/extensions/textBox.ts
+++ b/src/lib/editor/extensions/textBox.ts
@@ -2,7 +2,8 @@ import { Node, mergeAttributes } from '@tiptap/core';
 import type { CommandProps } from '@tiptap/core';
 import TextAlign from '@tiptap/extension-text-align';
 import type { Editor } from '@tiptap/core';
-import type { Node as PMNode, Slice } from '@tiptap/pm/model';
+import { DOMSerializer, Fragment } from '@tiptap/pm/model';
+import type { DOMOutputSpec, Node as PMNode, Schema, Slice } from '@tiptap/pm/model';
 import { NodeSelection, Selection, TextSelection, Plugin } from '@tiptap/pm/state';
 import type { EditorState } from '@tiptap/pm/state';
 import { Decoration, DecorationSet } from '@tiptap/pm/view';
@@ -112,6 +113,33 @@ function isDrawnShape(a: TextBoxAttrs): boolean {
   return !!SHAPES[a.shapeKind]?.points || !!a.shapePath || isLineKind(a.shapeKind);
 }
 
+// The blocks a copied box carries, read back off the span the clipboard form is.
+function clipboardContent(dom: HTMLElement, schema: Schema): Fragment {
+  try {
+    return Fragment.fromJSON(schema, JSON.parse(dom.getAttribute('data-tbx') || 'null'));
+  } catch {
+    return Fragment.empty;
+  }
+}
+
+// A box holds blocks, and in an HTML string any block tag inside a `<p>` closes it — so
+// a box copied to another window would arrive as loose paragraphs. It goes on the
+// clipboard as an inline span instead, its blocks in an attribute as JSON, its text
+// beside them for every reader that cannot take those back.
+function boxClipboardSerializer(schema: Schema): DOMSerializer {
+  const base = DOMSerializer.fromSchema(schema);
+  const box = base.nodes.textBox;
+  const nodes = {
+    ...base.nodes,
+    textBox: (node: PMNode) => {
+      const [, attrs] = box(node) as [string, Record<string, string>, 0];
+      return ['span', { ...attrs, 'data-tbx': JSON.stringify(node.content.toJSON()) },
+        node.textBetween(0, node.content.size, ' ')] as DOMOutputSpec;
+    },
+  };
+  return new DOMSerializer(nodes, base.marks);
+}
+
 export const TextBox = Node.create({
   name: 'textBox',
   // An inline node carrying block content, like the frame both formats write: it rides
@@ -230,7 +258,12 @@ export const TextBox = Node.create({
   },
 
   parseHTML() {
-    return [{ tag: 'div[data-textbox]' }];
+    return [
+      { tag: 'div[data-textbox]' },
+      // The clipboard's inline form, whose blocks ride an attribute (see
+      // boxClipboardSerializer); its own text is what the attribute already holds.
+      { tag: 'span[data-tbx]', getContent: (dom, schema) => clipboardContent(dom as HTMLElement, schema) },
+    ];
   },
 
   renderHTML({ HTMLAttributes, node }) {
@@ -343,6 +376,7 @@ export const TextBox = Node.create({
   // Show the resize frame + handles (via .textbox-active) whenever the caret sits
   // inside a box, so a plain click into it reveals the editing frame like an image.
   addProseMirrorPlugins() {
+    const clipboardSerializer = boxClipboardSerializer(this.editor.schema);
     return [
       new Plugin({
         // A selection may not end inside a box it did not start in: deleting one
@@ -377,6 +411,7 @@ export const TextBox = Node.create({
           return !carriesBox || !nestsBox(tr.doc);
         },
         props: {
+          clipboardSerializer,
           decorations(state) {
             const { from, to } = state.selection;
             const decos: Decoration[] = [];
diff --git a/tests/unit/text-box-guards.test.ts b/tests/unit/text-box-guards.test.ts
index 52786c7..7d3c18a 100644
--- a/tests/unit/text-box-guards.test.ts
+++ b/tests/unit/text-box-guards.test.ts
@@ -4,6 +4,7 @@
 // spill its text into the body).
 import { describe, it, expect } from 'vitest';
 import { Editor } from '@tiptap/core';
+import { __parseFromClipboard } from 'prosemirror-view';
 import Document from '@tiptap/extension-document';
 import Paragraph from '@tiptap/extension-paragraph';
 import Text from '@tiptap/extension-text';
@@ -214,3 +215,45 @@ describe('the frame as an atom', () => {
     ed.destroy();
   });
 });
+
+// Copying to another window goes through an HTML string, where any block tag inside a
+// <p> closes it — so the box travels as an inline span carrying its blocks as JSON.
+describe('a box on the clipboard', () => {
+  const copyPaste = (src: Editor, dst: Editor): void => {
+    const html = (src.view.serializeForClipboard(src.state.doc.slice(0, src.state.doc.content.size)) as
+      { dom: HTMLElement }).dom.innerHTML;
+    const slice = __parseFromClipboard(dst.view, '', html, false, dst.state.doc.resolve(1));
+    if (slice) dst.view.dispatch(dst.state.tr.replaceSelection(slice));
+  };
+
+  it('arrives in another editor as a box in the line', () => {
+    const src = makeEditor(...doc());
+    const dst = makeEditor({ type: 'paragraph' });
+    copyPaste(src, dst);
+    expect(dst.state.doc.childCount).toBe(1);
+    const para = dst.state.doc.child(0);
+    expect(para.content.child(1).type.name).toBe('textBox');
+    expect(para.content.child(1).textContent).toBe('KASTEN');
+    expect(para.textContent).toBe('vor AAA KASTEN nach BBB');
+    src.destroy();
+    dst.destroy();
+  });
+
+  it('keeps the frame\u2019s own size', () => {
+    const src = makeEditor(...doc());
+    const dst = makeEditor({ type: 'paragraph' });
+    copyPaste(src, dst);
+    expect(dst.state.doc.child(0).content.child(1).attrs).toMatchObject({ width: 160, height: 60 });
+    src.destroy();
+    dst.destroy();
+  });
+
+  it('reads as its plain text where the attribute cannot be taken back', () => {
+    const src = makeEditor(...doc());
+    const html = (src.view.serializeForClipboard(src.state.doc.slice(0, src.state.doc.content.size)) as
+      { dom: HTMLElement }).dom.innerHTML;
+    expect(html).toContain('KASTEN</span>');
+    expect(html).not.toContain('<div');
+    src.destroy();
+  });
+});