diff --git a/src/content-json-schema-defs.ts b/src/content-json-schema-defs.ts
index 15ec6fb..a2e123d 100644
--- a/src/content-json-schema-defs.ts
+++ b/src/content-json-schema-defs.ts
@@ -105,10 +105,10 @@ export const CONTENT_DEFS: Record<string, JsonSchema> = {
   ContentListMembership: {
     type: 'object',
     properties: {
-      numId: { type: 'string' },
+      numId: { type: 'string' }, // optional in the Zod source -- depth-only list membership (OOXML drawing paragraphs) carries no numbering identity
       level: { type: 'integer', minimum: 0, maximum: MAX_SAFE_INTEGER },
     },
-    required: ['numId', 'level'],
+    required: ['level'],
     additionalProperties: false,
   },
   ContentRun: {
diff --git a/src/content.test.ts b/src/content.test.ts
index a09982f..623cb1d 100644
--- a/src/content.test.ts
+++ b/src/content.test.ts
@@ -659,6 +659,33 @@ describe('ContentParagraphSchema headingLevel', () => {
   });
 });
 
+describe('ContentListMembership numId', () => {
+  it('parses a level-only membership, the shape a format with depth but no numbering identity produces (OOXML drawing paragraphs carry only a:pPr/@lvl)', () => {
+    const parsed = ContentParagraphSchema.parse({
+      kind: 'paragraph',
+      runs: [{ text: 'Bullet text' }],
+      list: { level: 1 },
+    });
+    expect(parsed.list).toEqual({ level: 1 });
+  });
+
+  it('still parses a numId+level membership, the shape a format with a shared numbering definition produces (docx w:numId, ODF minted identity)', () => {
+    const parsed = ContentParagraphSchema.parse({
+      kind: 'paragraph',
+      runs: [{ text: 'Item one' }],
+      list: { numId: '1', level: 0 },
+    });
+    expect(parsed.list).toEqual({ numId: '1', level: 0 });
+  });
+
+  it('keeps level required, so a membership without one does not parse', () => {
+    expect(ContentParagraphSchema.safeParse({ kind: 'paragraph', runs: [], list: { numId: '1' } }).success).toBe(
+      false,
+    );
+    expect(ContentParagraphSchema.safeParse({ kind: 'paragraph', runs: [], list: {} }).success).toBe(false);
+  });
+});
+
 describe('clampHeadingLevel', () => {
   it('leaves a level already within 1-6 untouched', () => {
     expect(clampHeadingLevel(1)).toBe(1);
diff --git a/src/content.ts b/src/content.ts
index 69b28a9..14f059c 100644
--- a/src/content.ts
+++ b/src/content.ts
@@ -31,7 +31,7 @@ export const ContentRunSchema = z.object({
 export type ContentRun = z.infer<typeof ContentRunSchema>;
 
 export const ContentListMembershipSchema = z.object({
-  numId: z.string(), // w:numId
+  numId: z.string().optional(), // identifies a shared numbering definition when the source format has one -- docx's w:numId, ODF's minted structural identity -- and is absent when the format carries only a depth (OOXML drawing paragraphs' a:pPr/@lvl), where fabricating one would invent numbering identity the source never had
   level: z.number().int().nonnegative(), // w:ilvl
 });
 export type ContentListMembership = z.infer<typeof ContentListMembershipSchema>;