diff --git a/src/lib/editor/extensions.ts b/src/lib/editor/extensions.ts
index 746d85c..06b5f50 100644
--- a/src/lib/editor/extensions.ts
+++ b/src/lib/editor/extensions.ts
@@ -79,7 +79,12 @@ import { Insertion, Deletion, TrackChanges } from './extensions/trackChanges';
 export const extensions = [
   // textBox and columns have their own groups so only the document (not
   // cells/lists/boxes) admits them; the note section is last or nowhere.
-  Document.extend({ content: '(block | textBox | columns)+ noteSection?' }),
+  // Spelled as an alternation, not `… + noteSection?`: with the trailing optional the
+  // match state after the first block offers noteSection first, and that is the type
+  // TipTap's clearNodes converts a block into (`contentMatchAt(i).defaultType`).
+  Document.extend({
+    content: '((block | textBox | columns)+ noteSection) | (block | textBox | columns)+',
+  }),
   Paragraph,
   Text,
   Bold,
diff --git a/tests/unit/doc-default-type.test.ts b/tests/unit/doc-default-type.test.ts
new file mode 100644
index 0000000..59fca03
--- /dev/null
+++ b/tests/unit/doc-default-type.test.ts
@@ -0,0 +1,26 @@
+import { describe, it, expect } from 'vitest';
+import { getSchema } from '@tiptap/core';
+import { extensions } from '../../src/lib/editor/extensions';
+
+// TipTap's clearNodes rewrites a block into its parent's `defaultType`, so the
+// document's must stay a paragraph at every index — noteSection there made every
+// style command on a block past the first throw (Invalid content for noteSection).
+describe('document content expression', () => {
+  it('offers a paragraph as the default type at every index', () => {
+    const schema = getSchema(extensions);
+    const p = schema.nodes.paragraph.createAndFill()!;
+    const doc = schema.nodes.doc.create(null, [p, p, p]);
+    for (let i = 0; i <= doc.childCount; i++) {
+      expect(doc.contentMatchAt(i).defaultType?.name).toBe('paragraph');
+    }
+  });
+
+  it('still admits a note section, last only', () => {
+    const schema = getSchema(extensions);
+    const p = schema.nodes.paragraph.createAndFill()!;
+    const note = schema.nodes.note.create(null, p);
+    const section = schema.nodes.noteSection.create(null, note);
+    expect(() => schema.nodes.doc.createChecked(null, [p, section])).not.toThrow();
+    expect(() => schema.nodes.doc.createChecked(null, [section, p])).toThrow();
+  });
+});