diff --git a/packages/layout-engine/painters/dom/src/features/math/converters/box.ts b/packages/layout-engine/painters/dom/src/features/math/converters/box.ts
new file mode 100644
index 0000000000..47cae2fa4c
--- /dev/null
+++ b/packages/layout-engine/painters/dom/src/features/math/converters/box.ts
@@ -0,0 +1,101 @@
+import type { MathObjectConverter } from '../types.js';
+
+const MATHML_NS = 'http://www.w3.org/1998/Math/MathML';
+
+/**
+ * Convert m:box (box / invisible grouping container) to MathML <mrow>.
+ *
+ * OMML structure:
+ *   m:box → m:boxPr (optional), m:e (content)
+ *
+ * MathML output:
+ *   <mrow> content </mrow>
+ *
+ * The box is purely a grouping mechanism with no visual rendering;
+ * it maps directly to MathML's <mrow>.
+ *
+ * @spec ECMA-376 §22.1.2.13
+ */
+export const convertBox: MathObjectConverter = (node, doc, convertChildren) => {
+  const elements = node.elements ?? [];
+  const base = elements.find((e) => e.name === 'm:e');
+
+  const mrow = doc.createElementNS(MATHML_NS, 'mrow');
+  mrow.appendChild(convertChildren(base?.elements ?? []));
+
+  return mrow.childNodes.length > 0 ? mrow : null;
+};
+
+/**
+ * Convert m:borderBox (bordered box) to MathML <menclose>.
+ *
+ * OMML structure:
+ *   m:borderBox → m:borderBoxPr (optional: m:hideTop, m:hideBot, m:hideLeft, m:hideRight,
+ *                                  m:strikeBLTR, m:strikeH, m:strikeTLBR, m:strikeV),
+ *                 m:e (content)
+ *
+ * MathML output:
+ *   <menclose notation="..."> content </menclose>
+ *
+ * By default all four borders are shown (notation="box"). Individual borders
+ * can be hidden via m:hide* flags, and diagonal/horizontal/vertical strikes
+ * can be added via m:strike* flags.
+ *
+ * @spec ECMA-376 §22.1.2.11
+ */
+export const convertBorderBox: MathObjectConverter = (node, doc, convertChildren) => {
+  const elements = node.elements ?? [];
+  const props = elements.find((e) => e.name === 'm:borderBoxPr');
+  const base = elements.find((e) => e.name === 'm:e');
+
+  /** OOXML ST_OnOff true values: "1", "on", "true", or boolean-flag presence. */
+  const isOn = (el?: { attributes?: Record<string, string> }) =>
+    el &&
+    (el.attributes?.['m:val'] === '1' ||
+      el.attributes?.['m:val'] === 'on' ||
+      el.attributes?.['m:val'] === 'true' ||
+      !el.attributes);
+
+  const hideTop = props?.elements?.find((e) => e.name === 'm:hideTop');
+  const hideBot = props?.elements?.find((e) => e.name === 'm:hideBot');
+  const hideLeft = props?.elements?.find((e) => e.name === 'm:hideLeft');
+  const hideRight = props?.elements?.find((e) => e.name === 'm:hideRight');
+  const strikeBLTR = props?.elements?.find((e) => e.name === 'm:strikeBLTR');
+  const strikeH = props?.elements?.find((e) => e.name === 'm:strikeH');
+  const strikeTLBR = props?.elements?.find((e) => e.name === 'm:strikeTLBR');
+  const strikeV = props?.elements?.find((e) => e.name === 'm:strikeV');
+
+  const notations: string[] = [];
+
+  const allHidden = isOn(hideTop) && isOn(hideBot) && isOn(hideLeft) && isOn(hideRight);
+
+  if (!allHidden) {
+    if (!isOn(hideTop) && !isOn(hideBot) && !isOn(hideLeft) && !isOn(hideRight)) {
+      notations.push('box');
+    } else {
+      if (!isOn(hideTop)) notations.push('top');
+      if (!isOn(hideBot)) notations.push('bottom');
+      if (!isOn(hideLeft)) notations.push('left');
+      if (!isOn(hideRight)) notations.push('right');
+    }
+  }
+
+  if (isOn(strikeBLTR)) notations.push('updiagonalstrike');
+  if (isOn(strikeH)) notations.push('horizontalstrike');
+  if (isOn(strikeTLBR)) notations.push('downdiagonalstrike');
+  if (isOn(strikeV)) notations.push('verticalstrike');
+
+  const content = convertChildren(base?.elements ?? []);
+
+  if (notations.length === 0) {
+    const mrow = doc.createElementNS(MATHML_NS, 'mrow');
+    mrow.appendChild(content);
+    return mrow;
+  }
+
+  const menclose = doc.createElementNS(MATHML_NS, 'menclose');
+  menclose.setAttribute('notation', notations.join(' '));
+  menclose.appendChild(content);
+
+  return menclose;
+};
diff --git a/packages/layout-engine/painters/dom/src/features/math/converters/index.ts b/packages/layout-engine/painters/dom/src/features/math/converters/index.ts
index 0e7eb25496..74aa424577 100644
--- a/packages/layout-engine/painters/dom/src/features/math/converters/index.ts
+++ b/packages/layout-engine/painters/dom/src/features/math/converters/index.ts
@@ -13,3 +13,4 @@ export { convertFunction } from './function.js';
 export { convertSubscript } from './subscript.js';
 export { convertSuperscript } from './superscript.js';
 export { convertSubSuperscript } from './sub-superscript.js';
+export { convertBox, convertBorderBox } from './box.js';
diff --git a/packages/layout-engine/painters/dom/src/features/math/omml-to-mathml.test.ts b/packages/layout-engine/painters/dom/src/features/math/omml-to-mathml.test.ts
index e689c8f842..bab5ef672a 100644
--- a/packages/layout-engine/painters/dom/src/features/math/omml-to-mathml.test.ts
+++ b/packages/layout-engine/painters/dom/src/features/math/omml-to-mathml.test.ts
@@ -927,3 +927,152 @@ describe('m:func converter', () => {
     expect(mis[1]!.textContent).toBe('cos');
   });
 });
+
+describe('m:box converter', () => {
+  it('converts m:box to <mrow>', () => {
+    const omml = {
+      name: 'm:oMath',
+      elements: [
+        {
+          name: 'm:box',
+          elements: [
+            {
+              name: 'm:e',
+              elements: [{ name: 'm:r', elements: [{ name: 'm:t', elements: [{ type: 'text', text: 'x' }] }] }],
+            },
+          ],
+        },
+      ],
+    };
+    const result = convertOmmlToMathml(omml, doc);
+    expect(result).not.toBeNull();
+    expect(result!.textContent).toBe('x');
+  });
+
+  it('returns null for empty m:box', () => {
+    const omml = {
+      name: 'm:oMath',
+      elements: [{ name: 'm:box', elements: [] }],
+    };
+    const result = convertOmmlToMathml(omml, doc);
+    expect(result).toBeNull();
+  });
+});
+
+describe('m:borderBox converter', () => {
+  it('converts m:borderBox to <menclose notation="box"> by default', () => {
+    const omml = {
+      name: 'm:oMath',
+      elements: [
+        {
+          name: 'm:borderBox',
+          elements: [
+            {
+              name: 'm:e',
+              elements: [{ name: 'm:r', elements: [{ name: 'm:t', elements: [{ type: 'text', text: 'E' }] }] }],
+            },
+          ],
+        },
+      ],
+    };
+    const result = convertOmmlToMathml(omml, doc);
+    expect(result).not.toBeNull();
+    const menclose = result!.querySelector('menclose');
+    expect(menclose).not.toBeNull();
+    expect(menclose!.getAttribute('notation')).toBe('box');
+    expect(menclose!.textContent).toBe('E');
+  });
+
+  it('hides individual sides when hide flags are set', () => {
+    const omml = {
+      name: 'm:oMath',
+      elements: [
+        {
+          name: 'm:borderBox',
+          elements: [
+            {
+              name: 'm:borderBoxPr',
+              elements: [
+                { name: 'm:hideTop', attributes: { 'm:val': '1' } },
+                { name: 'm:hideBot', attributes: { 'm:val': '1' } },
+              ],
+            },
+            {
+              name: 'm:e',
+              elements: [{ name: 'm:r', elements: [{ name: 'm:t', elements: [{ type: 'text', text: 'x' }] }] }],
+            },
+          ],
+        },
+      ],
+    };
+    const result = convertOmmlToMathml(omml, doc);
+    const menclose = result!.querySelector('menclose');
+    expect(menclose).not.toBeNull();
+    const notation = menclose!.getAttribute('notation')!;
+    expect(notation).toContain('left');
+    expect(notation).toContain('right');
+    expect(notation).not.toContain('top');
+    expect(notation).not.toContain('bottom');
+  });
+
+  it('adds strike notations', () => {
+    const omml = {
+      name: 'm:oMath',
+      elements: [
+        {
+          name: 'm:borderBox',
+          elements: [
+            {
+              name: 'm:borderBoxPr',
+              elements: [
+                { name: 'm:hideTop', attributes: { 'm:val': '1' } },
+                { name: 'm:hideBot', attributes: { 'm:val': '1' } },
+                { name: 'm:hideLeft', attributes: { 'm:val': '1' } },
+                { name: 'm:hideRight', attributes: { 'm:val': '1' } },
+                { name: 'm:strikeH', attributes: { 'm:val': '1' } },
+              ],
+            },
+            {
+              name: 'm:e',
+              elements: [{ name: 'm:r', elements: [{ name: 'm:t', elements: [{ type: 'text', text: 'y' }] }] }],
+            },
+          ],
+        },
+      ],
+    };
+    const result = convertOmmlToMathml(omml, doc);
+    const menclose = result!.querySelector('menclose');
+    expect(menclose).not.toBeNull();
+    expect(menclose!.getAttribute('notation')).toBe('horizontalstrike');
+  });
+
+  it('falls back to <mrow> when all borders hidden and no strikes', () => {
+    const omml = {
+      name: 'm:oMath',
+      elements: [
+        {
+          name: 'm:borderBox',
+          elements: [
+            {
+              name: 'm:borderBoxPr',
+              elements: [
+                { name: 'm:hideTop', attributes: { 'm:val': '1' } },
+                { name: 'm:hideBot', attributes: { 'm:val': '1' } },
+                { name: 'm:hideLeft', attributes: { 'm:val': '1' } },
+                { name: 'm:hideRight', attributes: { 'm:val': '1' } },
+              ],
+            },
+            {
+              name: 'm:e',
+              elements: [{ name: 'm:r', elements: [{ name: 'm:t', elements: [{ type: 'text', text: 'q' }] }] }],
+            },
+          ],
+        },
+      ],
+    };
+    const result = convertOmmlToMathml(omml, doc);
+    const menclose = result!.querySelector('menclose');
+    expect(menclose).toBeNull();
+    expect(result!.textContent).toBe('q');
+  });
+});
diff --git a/packages/layout-engine/painters/dom/src/features/math/omml-to-mathml.ts b/packages/layout-engine/painters/dom/src/features/math/omml-to-mathml.ts
index 1a5672d61d..ac8d5fefa4 100644
--- a/packages/layout-engine/painters/dom/src/features/math/omml-to-mathml.ts
+++ b/packages/layout-engine/painters/dom/src/features/math/omml-to-mathml.ts
@@ -18,6 +18,8 @@ import {
   convertSubscript,
   convertSuperscript,
   convertSubSuperscript,
+  convertBox,
+  convertBorderBox,
 } from './converters/index.js';
 
 export const MATHML_NS = 'http://www.w3.org/1998/Math/MathML';
@@ -47,8 +49,8 @@ const MATH_OBJECT_REGISTRY: Record<string, MathObjectConverter | null> = {
 
   // ── Not yet implemented (community contributions welcome) ────────────────
   'm:acc': null, // Accent (diacritical mark above base)
-  'm:borderBox': null, // Border box (border around math content)
-  'm:box': null, // Box (invisible grouping container)
+  'm:borderBox': convertBorderBox, // Border box (border around math content)
+  'm:box': convertBox, // Box (invisible grouping container)
   'm:d': null, // Delimiter (parentheses, brackets, braces)
   'm:eqArr': null, // Equation array (vertical array of equations)
   'm:groupChr': null, // Group character (overbrace, underbrace)