document DOMParser.parseFromString includeShadowRoots option

files/en-us/web/api/domparser/parsefromstring/index.md

@@ -13,7 +13,7 @@ The **`parseFromString()`** method of the {{domxref("DOMParser")}} interface par
 ## Syntax
 
 ```js-nolint
-parseFromString(string, mimeType)
+parseFromString(string, mimeType, options)
 ```
 
 ### Parameters
@@ -38,6 +38,16 @@ parseFromString(string, mimeType)
 
     Any other value is invalid and will cause a [`TypeError`](/en-US/docs/Web/JavaScript/Reference/Global_Objects/TypeError) to be thrown.
 
+- `options` (Optional)
+
+  - : An object. This object allows for additional configuration of the `parseFromString` method. Supported properties are:
+
+    - `includeShadowRoots` {{Non-standard_Inline}}
+
+    A value of `includeShadowRoots` enables parsing of HTML with Declarative Shadow Roots applied. This avoids some important security considerations as fragment parsing APIs like `innerHTML` or `insertAdjacentHTML()` don't support creation of Declarative Shadow Roots.
+
+> As `includeShadowRoots` is non-standard, once available [`setHTMLUnsafe` and `parseHTMLUnsafe`](https://github.com/mdn/mdn/issues/459) should be used instead.
+
 ### Return value
 
 An {{domxref("HTMLDocument")}} or an {{domxref("XMLDocument")}}, depending on the
@@ -93,6 +103,24 @@ if (errorNode) {
 
 Additionally, the parsing error may be reported to the browser's JavaScript console.
 
+### includeShadowRoots
+
+The below shows an example of passing `includeShadowRoots` as an option to `parseFromString`.
+
+```js
+<script>
+  const html = `
+    <div>
+      <template shadowrootmode="open"></template>
+    </div>
+  `;
+
+  const fragment = new DOMParser().parseFromString(html, 'text/html', {
+    includeShadowRoots: true
+  });
+</script>
+```
+
 ## Specifications
 
 {{Specifications}}