diff --git a/crates/obscura-js/js/bootstrap.js b/crates/obscura-js/js/bootstrap.js
index db39028..fb4b90c 100644
--- a/crates/obscura-js/js/bootstrap.js
+++ b/crates/obscura-js/js/bootstrap.js
@@ -663,6 +663,11 @@ class Node {
   get previousSibling() { return _wrap(+_dom("prev_sibling", this._nid)); }
   appendChild(c) {
     if (!c) return c;
+    if (c instanceof DocumentFragment) {
+      const children = Array.from(c.childNodes);
+      for (const child of children) this.appendChild(child);
+      return c;
+    }
     _dom("append_child", this._nid, c._nid);
     if (globalThis.__mutationObservers?.length) globalThis.__notifyMutation('childList', this._nid, [c._nid], []);
     if (c instanceof Element && c.tagName === 'SCRIPT') {
@@ -745,6 +750,12 @@ class Node {
   }
   replaceChild(newChild, oldChild) {
     if (!oldChild || !newChild) return oldChild;
+    if (newChild instanceof DocumentFragment) {
+      const children = Array.from(newChild.childNodes);
+      for (const child of children) this.insertBefore(child, oldChild);
+      this.removeChild(oldChild);
+      return oldChild;
+    }
     _dom("insert_before", newChild._nid, oldChild._nid);
     _dom("remove_child", oldChild._nid);
     return oldChild;
@@ -752,6 +763,11 @@ class Node {
   insertBefore(n, ref) {
     if (!n) return n;
     if (!ref) { this.appendChild(n); return n; }
+    if (n instanceof DocumentFragment) {
+      const children = Array.from(n.childNodes);
+      for (const child of children) this.insertBefore(child, ref);
+      return n;
+    }
     _dom("insert_before", n._nid, ref._nid);
     return n;
   }
diff --git a/crates/obscura-js/src/runtime.rs b/crates/obscura-js/src/runtime.rs
index eb9ecde..1f6e766 100644
--- a/crates/obscura-js/src/runtime.rs
+++ b/crates/obscura-js/src/runtime.rs
@@ -1377,6 +1377,112 @@ mod tests {
         );
     }
 
+    #[test]
+    fn append_child_flattens_document_fragment() {
+        let mut rt = setup_runtime(r#"<main id="host"></main>"#);
+        rt.run_page_init();
+        let result = rt
+            .evaluate(
+                r#"
+                const host = document.getElementById('host');
+                const fragment = document.createDocumentFragment();
+                const first = document.createElement('article');
+                const second = document.createElement('article');
+                first.id = 'first';
+                second.id = 'second';
+                first.className = second.className = 'quote';
+                fragment.appendChild(first);
+                fragment.appendChild(second);
+
+                const returned = host.appendChild(fragment);
+                return [
+                    returned === fragment,
+                    Array.from(host.children).map(node => node.id),
+                    host.querySelectorAll('.quote').length,
+                    fragment.childNodes.length,
+                    first.parentNode === host,
+                    first.parentElement === host,
+                ];
+                "#,
+            )
+            .unwrap();
+        assert_eq!(
+            result,
+            serde_json::json!([true, ["first", "second"], 2, 0, true, true])
+        );
+    }
+
+    #[test]
+    fn insert_before_flattens_document_fragment_in_order() {
+        let mut rt = setup_runtime(r#"<main id="host"><article id="last"></article></main>"#);
+        rt.run_page_init();
+        let result = rt
+            .evaluate(
+                r#"
+                const host = document.getElementById('host');
+                const last = document.getElementById('last');
+                const fragment = document.createDocumentFragment();
+                const first = document.createElement('article');
+                const second = document.createElement('article');
+                first.id = 'first';
+                second.id = 'second';
+                fragment.appendChild(first);
+                fragment.appendChild(second);
+
+                const returned = host.insertBefore(fragment, last);
+                return [
+                    returned === fragment,
+                    Array.from(host.children).map(node => node.id),
+                    fragment.childNodes.length,
+                    first.parentElement === host,
+                    second.parentElement === host,
+                ];
+                "#,
+            )
+            .unwrap();
+        assert_eq!(
+            result,
+            serde_json::json!([true, ["first", "second", "last"], 0, true, true])
+        );
+    }
+
+    #[test]
+    fn replace_child_flattens_document_fragment_and_removes_old_child() {
+        let mut rt = setup_runtime(
+            r#"<main id="host"><article id="old"></article><article id="tail"></article></main>"#,
+        );
+        rt.run_page_init();
+        let result = rt
+            .evaluate(
+                r#"
+                const host = document.getElementById('host');
+                const old = document.getElementById('old');
+                const fragment = document.createDocumentFragment();
+                const first = document.createElement('article');
+                const second = document.createElement('article');
+                first.id = 'first';
+                second.id = 'second';
+                fragment.appendChild(first);
+                fragment.appendChild(second);
+
+                const returned = host.replaceChild(fragment, old);
+                return [
+                    returned === old,
+                    Array.from(host.children).map(node => node.id),
+                    fragment.childNodes.length,
+                    old.parentNode === null,
+                    first.parentElement === host,
+                    second.parentElement === host,
+                ];
+                "#,
+            )
+            .unwrap();
+        assert_eq!(
+            result,
+            serde_json::json!([true, ["first", "second", "tail"], 0, true, true, true])
+        );
+    }
+
     #[test]
     fn test_inner_html() {
         let mut rt = setup_runtime(r#"<div id="x"><p>Hello</p></div>"#);