diff --git a/html5ever/examples/arena.rs b/html5ever/examples/arena.rs
index 36854caf..08ec7328 100644
--- a/html5ever/examples/arena.rs
+++ b/html5ever/examples/arena.rs
@@ -55,6 +55,7 @@ pub struct Node<'arena> {
 }
 
 /// HTML node data which can be an element, a comment, a string, a DOCTYPE, etc...
+#[derive(Clone)]
 pub enum NodeData<'arena> {
     Document,
     Doctype {
@@ -338,6 +339,21 @@ impl<'arena> TreeSink for Sink<'arena> {
             new_parent.append(child)
         }
     }
+
+    fn clone_subtree(&self, node: &Self::Handle) -> Self::Handle {
+        // Allocate the new node in the arena using Clone
+        let cloned_node = self.arena.alloc(Node::new(node.data.clone()));
+
+        // Clone all children and append them
+        let mut child = node.first_child.get();
+        while let Some(current_child) = child {
+            let cloned_child = self.clone_subtree(&current_child);
+            cloned_node.append(cloned_child);
+            child = current_child.next_sibling.get();
+        }
+
+        cloned_node
+    }
 }
 
 /// In this example an "arena" is created and filled with the DOM nodes.
@@ -352,5 +368,33 @@ fn main() {
     io::stdin().read_to_end(&mut bytes).unwrap();
 
     let arena = typed_arena::Arena::new();
-    html5ever_parse_slice_into_arena(&bytes, &arena);
+    let dom = html5ever_parse_slice_into_arena(&bytes, &arena);
+
+    // Print the DOM structure
+    print_node(dom, 0);
+}
+
+fn print_node<'arena>(node: &Node<'arena>, depth: usize) {
+    let indent = "  ".repeat(depth);
+
+    match &node.data {
+        NodeData::Document => println!("{}Document", indent),
+        NodeData::Doctype { name, .. } => println!("{}<!DOCTYPE {}>", indent, name),
+        NodeData::Text { contents } => {
+            let text = contents.borrow();
+            if !text.trim().is_empty() {
+                println!("{}\"{}\"", indent, text.trim());
+            }
+        },
+        NodeData::Comment { contents } => println!("{}<!-- {} -->", indent, contents),
+        NodeData::Element { name, .. } => println!("{}<{}>", indent, name.local),
+        NodeData::ProcessingInstruction { target, .. } => println!("{}<?{}>", indent, target),
+    }
+
+    // Print all children
+    let mut child = node.first_child.get();
+    while let Some(current_child) = child {
+        print_node(current_child, depth + 1);
+        child = current_child.next_sibling.get();
+    }
 }
diff --git a/html5ever/examples/noop-tree-builder.rs b/html5ever/examples/noop-tree-builder.rs
index f0673462..fc04e2b3 100644
--- a/html5ever/examples/noop-tree-builder.rs
+++ b/html5ever/examples/noop-tree-builder.rs
@@ -113,6 +113,11 @@ impl TreeSink for Sink {
     fn remove_from_parent(&self, _target: &usize) {}
     fn reparent_children(&self, _node: &usize, _new_parent: &usize) {}
     fn mark_script_already_started(&self, _node: &usize) {}
+
+    fn clone_subtree(&self, _node: &Self::Handle) -> Self::Handle {
+        // For this noop example, just return a new placeholder ID
+        self.get_id()
+    }
 }
 
 /// In this example we implement the TreeSink trait which takes each parsed elements and insert
diff --git a/html5ever/examples/print-tree-actions.rs b/html5ever/examples/print-tree-actions.rs
index dfa0aedd..3da79ea9 100644
--- a/html5ever/examples/print-tree-actions.rs
+++ b/html5ever/examples/print-tree-actions.rs
@@ -167,6 +167,12 @@ impl TreeSink for Sink {
     fn pop(&self, elem: &usize) {
         println!("Popped element {elem}");
     }
+
+    fn clone_subtree(&self, node: &Self::Handle) -> Self::Handle {
+        println!("Clone subtree for node {node}");
+        // For this example, just return a new placeholder ID
+        self.get_id()
+    }
 }
 
 /// Same example as the "noop-tree-builder", but this time every function implemented in our
diff --git a/html5ever/src/tree_builder/mod.rs b/html5ever/src/tree_builder/mod.rs
index f0d89b92..6a29478d 100644
--- a/html5ever/src/tree_builder/mod.rs
+++ b/html5ever/src/tree_builder/mod.rs
@@ -118,6 +118,9 @@ pub struct TreeBuilder<Handle, Sink> {
 
     /// Form element pointer.
     form_elem: RefCell<Option<Handle>>,
+
+    /// selectedcontent element pointer.
+    selectedcontent_elem: RefCell<Option<Handle>>,
     //§ END
     /// Frameset-ok flag.
     frameset_ok: Cell<bool>,
@@ -163,6 +166,7 @@ where
             active_formatting: Default::default(),
             head_elem: Default::default(),
             form_elem: Default::default(),
+            selectedcontent_elem: Default::default(),
             frameset_ok: Cell::new(true),
             ignore_lf: Default::default(),
             foster_parenting: Default::default(),
@@ -203,6 +207,7 @@ where
             active_formatting: Default::default(),
             head_elem: Default::default(),
             form_elem: RefCell::new(form_elem),
+            selectedcontent_elem: Default::default(),
             frameset_ok: Cell::new(true),
             ignore_lf: Default::default(),
             foster_parenting: Default::default(),
@@ -285,6 +290,10 @@ where
             tracer.trace_handle(form_elem);
         }
 
+        if let Some(selectedcontent_elem) = self.selectedcontent_elem.borrow().as_ref() {
+            tracer.trace_handle(selectedcontent_elem);
+        }
+
         if let Some(context_elem) = self.context_elem.borrow().as_ref() {
             tracer.trace_handle(context_elem);
         }
@@ -923,6 +932,7 @@ where
             .borrow_mut()
             .pop()
             .expect("no current element");
+
         self.sink.pop(&elem);
         elem
     }
@@ -1183,6 +1193,7 @@ where
         n
     }
 
+    /// Pop element until an element with the given name has been popped.
     fn pop_until_named(&self, name: LocalName) -> usize {
         self.pop_until(|p| *p.ns == ns!(html) && *p.local == name)
     }
@@ -1269,16 +1280,6 @@ where
                 _ => continue,
             };
             match *name {
-                local_name!("select") => {
-                    for ancestor in self.open_elems.borrow()[0..i].iter().rev() {
-                        if self.html_elem_named(ancestor, local_name!("template")) {
-                            return InsertionMode::InSelect;
-                        } else if self.html_elem_named(ancestor, local_name!("table")) {
-                            return InsertionMode::InSelectInTable;
-                        }
-                    }
-                    return InsertionMode::InSelect;
-                },
                 local_name!("td") | local_name!("th") => {
                     if !last {
                         return InsertionMode::InCell;
@@ -1401,6 +1402,12 @@ where
 
         self.insert_at(insertion_point, AppendNode(elem.clone()));
 
+        if qname.local == local_name!("selectedcontent")
+            && self.selectedcontent_elem.borrow().is_none()
+        {
+            *self.selectedcontent_elem.borrow_mut() = Some(elem.clone());
+        }
+
         match push {
             PushFlag::Push => self.push(&elem),
             PushFlag::NoPush => (),
@@ -1585,6 +1592,19 @@ where
         self.remove_from_stack(&node);
     }
 
+    fn maybe_clone_option_into_selectedcontent(&self, option: &Handle) {
+        if let Some(selectedcontent) = self.selectedcontent_elem.borrow().as_ref().cloned() {
+            self.clone_option_into_selectedcontent(option, &selectedcontent);
+        }
+    }
+
+    fn clone_option_into_selectedcontent(&self, option: &Handle, selectedcontent: &Handle) {
+        self.sink
+            .reparent_children(selectedcontent, &self.sink.get_document());
+        let cloned_option = self.sink.clone_subtree(option);
+        self.sink.reparent_children(&cloned_option, selectedcontent);
+    }
+
     //§ tree-construction
     fn is_foreign(&self, token: &Token) -> bool {
         if let Token::Eof = *token {
diff --git a/html5ever/src/tree_builder/rules.rs b/html5ever/src/tree_builder/rules.rs
index e0ddff45..fcbaf1f3 100644
--- a/html5ever/src/tree_builder/rules.rs
+++ b/html5ever/src/tree_builder/rules.rs
@@ -592,7 +592,7 @@ where
                     tag!(</address> | </article> | </aside> | </blockquote> | </button> | </center> |
                               </details> | </dialog> | </dir> | </div> | </dl> | </fieldset> | </figcaption> |
                               </figure> | </footer> | </header> | </hgroup> | </listing> | </main> | </menu> |
-                              </nav> | </ol> | </pre> | </search> | </section> | </summary> | </ul>),
+                              </nav> | </ol> | </pre> | </search> | </section> | </select> | </summary> | </ul>),
                 ) => {
                     if !self.in_scope_named(default_scope, tag.name.clone()) {
                         self.unexpected(&tag);
@@ -638,6 +638,30 @@ where
                     ProcessResult::Done
                 },
 
+                Token::Tag(tag @ tag!(</option>)) => {
+                    let option_in_stack = self
+                        .open_elems
+                        .borrow()
+                        .iter()
+                        .find(|elem| self.html_elem_named(elem, local_name!("option")))
+                        .cloned();
+
+                    self.process_end_tag_in_body(tag);
+
+                    if let Some(option) = option_in_stack {
+                        if !self
+                            .open_elems
+                            .borrow()
+                            .iter()
+                            .any(|elem| self.sink.same_node(elem, &option))
+                        {
+                            self.maybe_clone_option_into_selectedcontent(&option);
+                        }
+                    }
+
+                    ProcessResult::Done
+                },
+
                 Token::Tag(tag!(</p>)) => {
                     if !self.in_scope_named(button_scope, local_name!("p")) {
                         self.sink.parse_error(Borrowed("No <p> tag to close"));
@@ -753,18 +777,37 @@ where
                     )
                 },
 
-                Token::Tag(
-                    tag @ tag!(<area> | <br> | <embed> | <img> | <keygen> | <wbr> | <input>),
-                ) => {
-                    let keep_frameset_ok = match tag.name {
-                        local_name!("input") => self.is_type_hidden(&tag),
-                        _ => false,
-                    };
+                Token::Tag(tag @ tag!(<area> | <br> | <embed> | <img> | <keygen> | <wbr>)) => {
                     self.reconstruct_active_formatting_elements();
                     self.insert_and_pop_element_for(tag);
-                    if !keep_frameset_ok {
+                    self.frameset_ok.set(false);
+                    ProcessResult::DoneAckSelfClosing
+                },
+
+                Token::Tag(tag @ tag!(<input>)) => {
+                    if self.is_fragment()
+                        && self.html_elem_named(
+                            self.context_elem.borrow().as_ref().unwrap(),
+                            local_name!("select"),
+                        )
+                    {
+                        self.unexpected(&tag);
+                    }
+
+                    if self.in_scope_named(default_scope, local_name!("select")) {
+                        self.unexpected(&tag);
+                        self.pop_until_named(local_name!("select"));
+                    }
+
+                    let is_type_hidden = self.is_type_hidden(&tag);
+
+                    self.reconstruct_active_formatting_elements();
+                    self.insert_and_pop_element_for(tag);
+
+                    if !is_type_hidden {
                         self.frameset_ok.set(false);
                     }
+
                     ProcessResult::DoneAckSelfClosing
                 },
 
@@ -775,6 +818,15 @@ where
 
                 Token::Tag(tag @ tag!(<hr>)) => {
                     self.close_p_element_in_button_scope();
+                    if self.in_scope_named(default_scope, local_name!("select")) {
+                        self.generate_implied_end_tags(cursory_implied_end);
+                        if self.in_scope_named(default_scope, local_name!("option"))
+                            || self.in_scope_named(default_scope, local_name!("optgroup"))
+                        {
+                            self.sink.parse_error(Borrowed("hr in option"));
+                        }
+                    }
+
                     self.insert_and_pop_element_for(tag);
                     self.frameset_ok.set(false);
                     ProcessResult::DoneAckSelfClosing
@@ -813,26 +865,52 @@ where
 
                 // <noscript> handled in wildcard case below
                 Token::Tag(tag @ tag!(<select>)) => {
+                    if self.is_fragment()
+                        && self.html_elem_named(
+                            self.context_elem.borrow().as_ref().unwrap(),
+                            local_name!("select"),
+                        )
+                    {
+                        self.unexpected(&tag);
+                    } else if self.in_scope_named(default_scope, local_name!("select")) {
+                        self.unexpected(&tag);
+                        self.pop_until_named(local_name!("select"));
+                    } else {
+                        self.reconstruct_active_formatting_elements();
+                        self.insert_element_for(tag);
+                        self.frameset_ok.set(false);
+                    }
+
+                    ProcessResult::Done
+                },
+
+                Token::Tag(tag @ tag!(<option>)) => {
+                    if self.in_scope_named(default_scope, local_name!("select")) {
+                        self.generate_implied_end_except(local_name!("optgroup"));
+                        if self.in_scope_named(default_scope, local_name!("option")) {
+                            self.sink.parse_error(Borrowed("nested options"));
+                        }
+                    } else if self.current_node_named(local_name!("option")) {
+                        self.pop();
+                    }
+
                     self.reconstruct_active_formatting_elements();
                     self.insert_element_for(tag);
-                    self.frameset_ok.set(false);
-                    // NB: mode == InBody but possibly self.mode != mode, if
-                    // we're processing "as in the rules for InBody".
-                    self.mode.set(match self.mode.get() {
-                        InsertionMode::InTable
-                        | InsertionMode::InCaption
-                        | InsertionMode::InTableBody
-                        | InsertionMode::InRow
-                        | InsertionMode::InCell => InsertionMode::InSelectInTable,
-                        _ => InsertionMode::InSelect,
-                    });
                     ProcessResult::Done
                 },
 
-                Token::Tag(tag @ tag!(<optgroup> | <option>)) => {
-                    if self.current_node_named(local_name!("option")) {
+                Token::Tag(tag @ tag!(<optgroup>)) => {
+                    if self.in_scope_named(default_scope, local_name!("select")) {
+                        self.generate_implied_end_tags(cursory_implied_end);
+                        if self.in_scope_named(default_scope, local_name!("option"))
+                            || self.in_scope_named(default_scope, local_name!("optgroup"))
+                        {
+                            self.sink.parse_error(Borrowed("nested options"));
+                        }
+                    } else if self.current_node_named(local_name!("option")) {
                         self.pop();
                     }
+
                     self.reconstruct_active_formatting_elements();
                     self.insert_element_for(tag);
                     ProcessResult::Done
@@ -1286,133 +1364,6 @@ where
                 token => self.step(InsertionMode::InBody, token),
             },
 
-            // § parsing-main-inselect
-            // TODO: not in spec?
-            InsertionMode::InSelect => match token {
-                Token::NullCharacter => self.unexpected(&token),
-                Token::Characters(_, text) => self.append_text(text),
-                Token::Comment(text) => self.append_comment(text),
-
-                Token::Tag(tag!(<html>)) => self.step(InsertionMode::InBody, token),
-
-                Token::Tag(tag @ tag!(<option>)) => {
-                    if self.current_node_named(local_name!("option")) {
-                        self.pop();
-                    }
-                    self.insert_element_for(tag);
-                    ProcessResult::Done
-                },
-
-                Token::Tag(tag @ tag!(<optgroup>)) => {
-                    if self.current_node_named(local_name!("option")) {
-                        self.pop();
-                    }
-                    if self.current_node_named(local_name!("optgroup")) {
-                        self.pop();
-                    }
-                    self.insert_element_for(tag);
-                    ProcessResult::Done
-                },
-
-                Token::Tag(tag @ tag!(<hr>)) => {
-                    if self.current_node_named(local_name!("option")) {
-                        self.pop();
-                    }
-                    if self.current_node_named(local_name!("optgroup")) {
-                        self.pop();
-                    }
-                    self.insert_element_for(tag);
-                    self.pop();
-                    ProcessResult::DoneAckSelfClosing
-                },
-
-                Token::Tag(tag!( </optgroup>)) => {
-                    if self.open_elems.borrow().len() >= 2
-                        && self.current_node_named(local_name!("option"))
-                        && self.html_elem_named(
-                            &self.open_elems.borrow()[self.open_elems.borrow().len() - 2],
-                            local_name!("optgroup"),
-                        )
-                    {
-                        self.pop();
-                    }
-                    if self.current_node_named(local_name!("optgroup")) {
-                        self.pop();
-                    } else {
-                        self.unexpected(&token);
-                    }
-                    ProcessResult::Done
-                },
-
-                Token::Tag(tag!(</option>)) => {
-                    if self.current_node_named(local_name!("option")) {
-                        self.pop();
-                    } else {
-                        self.unexpected(&token);
-                    }
-                    ProcessResult::Done
-                },
-
-                Token::Tag(tag @ tag!(<select> | </select>)) => {
-                    let in_scope = self.in_scope_named(select_scope, local_name!("select"));
-
-                    if !in_scope || tag.kind == StartTag {
-                        self.unexpected(&tag);
-                    }
-
-                    if in_scope {
-                        self.pop_until_named(local_name!("select"));
-                        self.mode.set(self.reset_insertion_mode());
-                    }
-                    ProcessResult::Done
-                },
-
-                Token::Tag(tag!(<input> | <keygen> | <textarea>)) => {
-                    self.unexpected(&token);
-                    if self.in_scope_named(select_scope, local_name!("select")) {
-                        self.pop_until_named(local_name!("select"));
-                        ProcessResult::Reprocess(self.reset_insertion_mode(), token)
-                    } else {
-                        ProcessResult::Done
-                    }
-                },
-
-                Token::Tag(tag!(<script> | <template> | </template>)) => {
-                    self.step(InsertionMode::InHead, token)
-                },
-
-                Token::Eof => self.step(InsertionMode::InBody, token),
-
-                token => self.unexpected(&token),
-            },
-
-            // § parsing-main-inselectintable
-            // TODO: not in spec?
-            InsertionMode::InSelectInTable => match token {
-                Token::Tag(
-                    tag!(<caption> | <table> | <tbody> | <tfoot> | <thead> | <tr> | <td> | <th>),
-                ) => {
-                    self.unexpected(&token);
-                    self.pop_until_named(local_name!("select"));
-                    ProcessResult::Reprocess(self.reset_insertion_mode(), token)
-                },
-
-                Token::Tag(
-                    tag @
-                    tag!(</caption> | </table> | </tbody> | </tfoot> | </thead> | </tr> | </td> | </th>),
-                ) => {
-                    self.unexpected(&tag);
-                    if self.in_scope_named(table_scope, tag.name.clone()) {
-                        self.pop_until_named(local_name!("select"));
-                        ProcessResult::Reprocess(self.reset_insertion_mode(), Token::Tag(tag))
-                    } else {
-                        ProcessResult::Done
-                    }
-                },
-
-                token => self.step(InsertionMode::InSelect, token),
-            },
-
             // § The "in template" insertion mode
             // https://html.spec.whatwg.org/multipage/parsing.html#parsing-main-intemplate
             InsertionMode::InTemplate => match token {
diff --git a/html5ever/src/tree_builder/tag_sets.rs b/html5ever/src/tree_builder/tag_sets.rs
index 7c8aab1c..47fece1c 100644
--- a/html5ever/src/tree_builder/tag_sets.rs
+++ b/html5ever/src/tree_builder/tag_sets.rs
@@ -48,13 +48,9 @@ macro_rules! declare_tag_set (
 pub(crate) fn empty_set(_: ExpandedName) -> bool {
     false
 }
-#[inline(always)]
-pub(crate) fn full_set(_: ExpandedName) -> bool {
-    true
-}
 
 declare_tag_set!(pub html_default_scope =
-    "applet" "caption" "html" "table" "td" "th" "marquee" "object" "template");
+    "applet" "caption" "html" "table" "td" "th" "marquee" "object" "select" "template");
 
 #[inline(always)]
 pub(crate) fn default_scope(name: ExpandedName) -> bool {
@@ -66,7 +62,6 @@ pub(crate) fn default_scope(name: ExpandedName) -> bool {
 declare_tag_set!(pub list_item_scope = [default_scope] + "ol" "ul");
 declare_tag_set!(pub button_scope = [default_scope] + "button");
 declare_tag_set!(pub table_scope = "html" "table" "template");
-declare_tag_set!(pub select_scope = [full_set] - "optgroup" "option");
 
 declare_tag_set!(pub table_body_context = "tbody" "tfoot" "thead" "template" "html");
 declare_tag_set!(pub table_row_context = "tr" "template" "html");
diff --git a/html5ever/src/tree_builder/types.rs b/html5ever/src/tree_builder/types.rs
index 684d5b0b..525608c2 100644
--- a/html5ever/src/tree_builder/types.rs
+++ b/html5ever/src/tree_builder/types.rs
@@ -31,8 +31,6 @@ pub(crate) enum InsertionMode {
     InTableBody,
     InRow,
     InCell,
-    InSelect,
-    InSelectInTable,
     InTemplate,
     AfterBody,
     InFrameset,
diff --git a/markup5ever/interface/tree_builder.rs b/markup5ever/interface/tree_builder.rs
index 378a57ce..107dc94c 100644
--- a/markup5ever/interface/tree_builder.rs
+++ b/markup5ever/interface/tree_builder.rs
@@ -236,6 +236,9 @@ pub trait TreeSink {
     /// Remove all the children from node and append them to new_parent.
     fn reparent_children(&self, node: &Self::Handle, new_parent: &Self::Handle);
 
+    /// Clone a node and all its descendants, returning the cloned node.
+    fn clone_subtree(&self, node: &Self::Handle) -> Self::Handle;
+
     /// Returns true if the adjusted current node is an HTML integration point
     /// and the token is a start tag.
     fn is_mathml_annotation_xml_integration_point(&self, _handle: &Self::Handle) -> bool {
diff --git a/rcdom/html5lib-tests b/rcdom/html5lib-tests
index a9f44960..f994590f 160000
--- a/rcdom/html5lib-tests
+++ b/rcdom/html5lib-tests
@@ -1 +1 @@
-Subproject commit a9f44960a9fedf265093d22b2aa3c7ca123727b9
+Subproject commit f994590f528ac8b6073665791ddb1ed85c66dfb2
diff --git a/rcdom/lib.rs b/rcdom/lib.rs
index 2cc65ae1..3b6b22fc 100644
--- a/rcdom/lib.rs
+++ b/rcdom/lib.rs
@@ -60,7 +60,7 @@ use markup5ever::ExpandedName;
 use markup5ever::QualName;
 
 /// The different kinds of nodes in the DOM.
-#[derive(Debug)]
+#[derive(Debug, Clone)]
 pub enum NodeData {
     /// The `Document` itself - the root node of a HTML document.
     Document,
@@ -417,6 +417,18 @@ impl TreeSink for RcDom {
         new_children.extend(mem::take(&mut *children));
     }
 
+    fn clone_subtree(&self, node: &Handle) -> Handle {
+        let cloned_node = Node::new(node.data.clone());
+
+        // Clone all children recursively
+        for child in node.children.borrow().iter() {
+            let cloned_child = self.clone_subtree(child);
+            append(&cloned_node, cloned_child);
+        }
+
+        cloned_node
+    }
+
     fn is_mathml_annotation_xml_integration_point(&self, target: &Handle) -> bool {
         if let NodeData::Element {
             mathml_annotation_xml_integration_point,
diff --git a/rcdom/tests/html-tree-builder.rs b/rcdom/tests/html-tree-builder.rs
index 0ba6d086..be611aa7 100644
--- a/rcdom/tests/html-tree-builder.rs
+++ b/rcdom/tests/html-tree-builder.rs
@@ -189,14 +189,16 @@ fn make_test_desc_with_scripting_flag(
     fields: &HashMap<String, String>,
     scripting_enabled: bool,
 ) -> Test {
-    let get_field = |key| {
-        let field = fields.get(key).expect("missing field");
-        field.trim_end_matches('\n').to_string()
+    let expect_field = |key| {
+        fields
+            .get(key)
+            .unwrap_or_else(|| panic!("missing field {}, testcase: {:?}", key, fields))
+            .to_string()
     };
 
-    let mut data = fields.get("data").expect("missing data").to_string();
+    let mut data = expect_field("data");
     data.pop();
-    let expected = get_field("document");
+    let expected = expect_field("document").trim_end_matches('\n').to_string();
     let context = fields
         .get("document-fragment")
         .map(|field| context_name(field.trim_end_matches('\n')));
diff --git a/rcdom/tests/html-tree-sink.rs b/rcdom/tests/html-tree-sink.rs
index c5371593..77803407 100644
--- a/rcdom/tests/html-tree-sink.rs
+++ b/rcdom/tests/html-tree-sink.rs
@@ -4,7 +4,7 @@ use html5ever::tendril::StrTendril;
 use html5ever::ExpandedName;
 use html5ever::QualName;
 use markup5ever::interface::{ElementFlags, NodeOrText, QuirksMode, TreeSink};
-use markup5ever::{local_name, ns, Attribute};
+use markup5ever::{local_name, ns, Attribute, LocalName};
 use markup5ever_rcdom::{Handle, RcDom};
 use std::borrow::Cow;
 use std::cell::{Cell, RefCell};
@@ -111,6 +111,10 @@ impl TreeSink for LineCountingDOM {
     fn set_current_line(&self, line_number: u64) {
         self.current_line.set(line_number);
     }
+
+    fn clone_subtree(&self, node: &Self::Handle) -> Self::Handle {
+        self.rcdom.clone_subtree(node)
+    }
 }
 
 #[test]
diff --git a/web_atoms/local_names.txt b/web_atoms/local_names.txt
index 1c4b39b5..936f543a 100644
--- a/web_atoms/local_names.txt
+++ b/web_atoms/local_names.txt
@@ -879,6 +879,7 @@ section
 seed
 select
 selected
+selectedcontent
 selection
 selector
 semantics