(* HTML5 Tree Builder *)

module Dom = Dom
module Token = Tokenizer_token
module State = Tokenizer_state

type fragment_context = {
  tag_name : string;
  namespace : string option;
}

type formatting_entry =
  | Marker
  | Entry of {
      name : string;
      attrs : (string * string) list;
      node : Dom.node;
    }

type parse_error = {
  code : Parse_error_code.t;
  line : int;
  column : int;
}

type t = {
  mutable document : Dom.node;
  mutable mode : Parser_insertion_mode.t;
  mutable original_mode : Parser_insertion_mode.t option;
  mutable open_elements : Dom.node list;
  mutable active_formatting : formatting_entry list;
  mutable head_element : Dom.node option;
  mutable form_element : Dom.node option;
  mutable frameset_ok : bool;
  mutable ignore_lf : bool;
  mutable foster_parenting : bool;
  mutable pending_table_chars : string list;
  mutable template_modes : Parser_insertion_mode.t list;
  mutable quirks_mode : Dom.quirks_mode;
  mutable errors : parse_error list;
  collect_errors : bool;
  fragment_context : fragment_context option;
  mutable fragment_context_element : Dom.node option;
  iframe_srcdoc : bool;
  mutable current_line : int;
  mutable current_column : int;
}

let create ?(collect_errors=false) ?fragment_context ?(iframe_srcdoc=false) () =
  let is_fragment = fragment_context <> None in
  let doc = if is_fragment then Dom.create_document_fragment () else Dom.create_document () in
  let t = {
    document = doc;
    mode = Parser_insertion_mode.Initial;
    original_mode = None;
    open_elements = [];
    active_formatting = [];
    head_element = None;
    form_element = None;
    frameset_ok = true;
    ignore_lf = false;
    foster_parenting = false;
    pending_table_chars = [];
    template_modes = [];
    quirks_mode = Dom.No_quirks;
    errors = [];
    collect_errors;
    fragment_context;
    fragment_context_element = None;
    iframe_srcdoc;
    current_line = 1;
    current_column = 1;
  } in
  (* Initialize fragment parsing *)
  (match fragment_context with
  | Some ctx ->
    let name = String.lowercase_ascii ctx.tag_name in
    let ns = ctx.namespace in
    (* Create html root *)
    let root = Dom.create_element "html" () in
    Dom.append_child doc root;
    t.open_elements <- [root];
    (* For foreign content contexts, create context element *)
    (match ns with
    | Some namespace when namespace <> "html" ->
      let context_elem = Dom.create_element ctx.tag_name ~namespace:ns () in
      Dom.append_child root context_elem;
      t.open_elements <- [context_elem; root];
      t.fragment_context_element <- Some context_elem
    | _ -> ());
    (* Set initial mode based on context *)
    t.mode <- (
      if name = "html" then Parser_insertion_mode.Before_head
      else if Parser_constants.is_table_section_element name && (ns = None || ns = Some "html") then
        Parser_insertion_mode.In_table_body
      else if name = "tr" && (ns = None || ns = Some "html") then
        Parser_insertion_mode.In_row
      else if Parser_constants.is_table_cell_element name && (ns = None || ns = Some "html") then
        Parser_insertion_mode.In_cell
      else if name = "caption" && (ns = None || ns = Some "html") then
        Parser_insertion_mode.In_caption
      else if name = "colgroup" && (ns = None || ns = Some "html") then
        Parser_insertion_mode.In_column_group
      else if name = "table" && (ns = None || ns = Some "html") then
        Parser_insertion_mode.In_table
      else if name = "template" && (ns = None || ns = Some "html") then begin
        t.template_modes <- [Parser_insertion_mode.In_template];
        Parser_insertion_mode.In_template
      end
      else
        Parser_insertion_mode.In_body
    );
    t.frameset_ok <- false
  | None -> ());
  t

(* Position tracking for error reporting *)
let set_position t ~line ~column =
  t.current_line <- line;
  t.current_column <- column

(* Error handling *)
let parse_error t code =
  if t.collect_errors then
    t.errors <- { code = Parse_error_code.of_string code; line = t.current_line; column = t.current_column } :: t.errors

(* Stack helpers *)
let current_node t =
  match t.open_elements with
  | [] -> None
  | x :: _ -> Some x

let adjusted_current_node t =
  match t.fragment_context, t.open_elements with
  | Some ctx, [_] ->
    (* Fragment case: use context element info *)
    Some (Dom.create_element ctx.tag_name ~namespace:ctx.namespace ())
  | _, x :: _ -> Some x
  | _, [] -> None

let is_in_html_namespace node =
  node.Dom.namespace = None || node.Dom.namespace = Some "html"

(* Namespace-aware check for "special" elements per WHATWG spec *)
let is_special_element node =
  let name = String.lowercase_ascii node.Dom.name in
  match node.Dom.namespace with
  | None | Some "html" -> Parser_constants.is_special name
  | Some "mathml" -> List.mem name ["mi"; "mo"; "mn"; "ms"; "mtext"; "annotation-xml"]
  | Some "svg" -> List.mem name ["foreignobject"; "desc"; "title"]
  | _ -> false

let adjusted_current_node_in_html_namespace t =
  match adjusted_current_node t with
  | Some node -> is_in_html_namespace node
  | None -> true

(* Insertion helpers *)
let appropriate_insertion_place t =
  match current_node t with
  | None -> (t.document, None)
  | Some target ->
    if t.foster_parenting && Parser_constants.is_foster_parenting_element target.Dom.name then begin
      (* Foster parenting per WHATWG spec *)
      (* Step 1: Find last (most recent) template and table in stack *)
      (* Note: index 0 = top of stack = most recently added *)
      let last_template_idx = ref None in
      let last_table_idx = ref None in
      List.iteri (fun i n ->
        (* Take first match (most recent = lowest index) *)
        if n.Dom.name = "template" && !last_template_idx = None then last_template_idx := Some i;
        if n.Dom.name = "table" && !last_table_idx = None then last_table_idx := Some i
      ) t.open_elements;

      (* Step 2-3: If last template is more recent than last table (lower index = more recent) *)
      match !last_template_idx, !last_table_idx with
      | Some ti, None ->
        (* No table, use template content *)
        let template = List.nth t.open_elements ti in
        (match template.Dom.template_content with
         | Some tc -> (tc, None)
         | None -> (template, None))
      | Some ti, Some tbi when ti < tbi ->
        (* Template is more recent than table, use template content *)
        let template = List.nth t.open_elements ti in
        (match template.Dom.template_content with
         | Some tc -> (tc, None)
         | None -> (template, None))
      | _, Some tbi ->
        (* Use table's parent as foster parent *)
        let table = List.nth t.open_elements tbi in
        (match table.Dom.parent with
         | Some parent -> (parent, Some table)
         | None ->
           (* Step 6: element above table in stack (index + 1 since 0 is top) *)
           if tbi + 1 < List.length t.open_elements then
             (List.nth t.open_elements (tbi + 1), None)
           else
             (t.document, None))
      | None, None ->
        (* No table or template, use document *)
        (t.document, None)
    end else begin
      (* If target is a template, insert into its content document fragment *)
      match target.Dom.template_content with
      | Some tc -> (tc, None)
      | None -> (target, None)
    end

let insert_element t name ?(namespace=None) ?(push=false) attrs =
  let location = Dom.make_location ~line:t.current_line ~column:t.current_column () in
  let node = Dom.create_element name ~namespace ~attrs ~location () in
  let (parent, before) = appropriate_insertion_place t in
  (match before with
   | None -> Dom.append_child parent node
   | Some ref -> Dom.insert_before parent node ref);
  if push then t.open_elements <- node :: t.open_elements;
  node

let insert_element_for_token t (tag : Token.tag) =
  insert_element t tag.name ~push:true tag.attrs

let insert_foreign_element t (tag : Token.tag) namespace =
  let attrs =
    if namespace = Some "svg" then
      Parser_constants.adjust_svg_attrs (Parser_constants.adjust_foreign_attrs tag.attrs)
    else
      Parser_constants.adjust_foreign_attrs tag.attrs
  in
  let name =
    if namespace = Some "svg" then Parser_constants.adjust_svg_tag_name tag.name
    else tag.name
  in
  let node = insert_element t name ~namespace attrs in
  t.open_elements <- node :: t.open_elements;
  node

let insert_character t data =
  if t.ignore_lf && String.length data > 0 && data.[0] = '\n' then begin
    t.ignore_lf <- false;
    if String.length data > 1 then begin
      let rest = String.sub data 1 (String.length data - 1) in
      let (parent, before) = appropriate_insertion_place t in
      Dom.insert_text_at parent rest before
    end
  end else begin
    t.ignore_lf <- false;
    let (parent, before) = appropriate_insertion_place t in
    Dom.insert_text_at parent data before
  end

let insert_comment t data =
  let location = Dom.make_location ~line:t.current_line ~column:t.current_column () in
  let node = Dom.create_comment ~location data in
  let (parent, _) = appropriate_insertion_place t in
  Dom.append_child parent node

let insert_comment_to_document t data =
  let location = Dom.make_location ~line:t.current_line ~column:t.current_column () in
  let node = Dom.create_comment ~location data in
  Dom.append_child t.document node

(* Stack manipulation *)
let pop_current t =
  match t.open_elements with
  | [] -> ()
  | _ :: rest -> t.open_elements <- rest

let pop_until t pred =
  let rec loop () =
    match t.open_elements with
    | [] -> ()
    | x :: rest ->
      t.open_elements <- rest;
      if not (pred x) then loop ()
  in
  loop ()

let pop_until_tag t name =
  pop_until t (fun n -> n.Dom.name = name)

(* Pop until HTML namespace element with given name *)
let pop_until_html_tag t name =
  pop_until t (fun n -> n.Dom.name = name && is_in_html_namespace n)

let pop_until_one_of t names =
  pop_until t (fun n -> List.mem n.Dom.name names)

(* Pop until HTML namespace element with one of given names *)
let pop_until_html_one_of t names =
  pop_until t (fun n -> List.mem n.Dom.name names && is_in_html_namespace n)

(* Check if element is an HTML integration point *)
let is_html_integration_point node =
  (* SVG foreignObject, desc, and title are always HTML integration points *)
  if node.Dom.namespace = Some "svg" &&
     Parser_constants.is_svg_html_integration node.Dom.name then true
  (* annotation-xml is an HTML integration point only with specific encoding values *)
  else if node.Dom.namespace = Some "mathml" && node.Dom.name = "annotation-xml" then
    match List.assoc_opt "encoding" node.Dom.attrs with
    | Some enc ->
      let enc_lower = String.lowercase_ascii enc in
      enc_lower = "text/html" || enc_lower = "application/xhtml+xml"
    | None -> false
  else false

(* Check if element is a MathML text integration point *)
let is_mathml_text_integration_point node =
  node.Dom.namespace = Some "mathml" &&
  Parser_constants.is_mathml_text_integration node.Dom.name

(* Scope checks - integration points also terminate scope (except for table scope) *)
(* Per WHATWG spec, scope checks only consider HTML namespace elements for the target names *)
let has_element_in_scope_impl t names exclude_list ~check_integration_points =
  let rec check = function
    | [] -> false
    | n :: rest ->
      (* Target elements must be in HTML namespace *)
      if is_in_html_namespace n && List.mem n.Dom.name names then true
      else if is_in_html_namespace n && List.mem n.Dom.name exclude_list then false
      (* Integration points terminate scope (unless we're checking table scope) *)
      else if check_integration_points && (is_html_integration_point n || is_mathml_text_integration_point n) then false
      else check rest
  in
  check t.open_elements

let has_element_in_scope t name =
  has_element_in_scope_impl t [name] Parser_constants.default_scope ~check_integration_points:true

let has_element_in_button_scope t name =
  has_element_in_scope_impl t [name] Parser_constants.button_scope ~check_integration_points:true

let has_element_in_list_item_scope t name =
  has_element_in_scope_impl t [name] Parser_constants.list_item_scope ~check_integration_points:true

let has_element_in_table_scope t name =
  has_element_in_scope_impl t [name] Parser_constants.table_scope ~check_integration_points:false

let has_element_in_select_scope t name =
  let rec check = function
    | [] -> false
    | n :: rest ->
      if n.Dom.name = name then true
      else if not (Parser_constants.is_select_scope_exclude n.Dom.name) then false
      else check rest
  in
  check t.open_elements

(* Implied end tags *)
let generate_implied_end_tags t ?except () =
  let rec loop () =
    match current_node t with
    | Some n when Parser_constants.is_implied_end_tag n.Dom.name ->
      (match except with
       | Some ex when n.Dom.name = ex -> ()
       | _ -> pop_current t; loop ())
    | _ -> ()
  in
  loop ()

let generate_all_implied_end_tags t =
  let rec loop () =
    match current_node t with
    | Some n when Parser_constants.is_thoroughly_implied_end_tag n.Dom.name ->
      pop_current t; loop ()
    | _ -> ()
  in
  loop ()

(* Active formatting elements *)
let push_formatting_marker t =
  t.active_formatting <- Marker :: t.active_formatting

let push_formatting_element t node name attrs =
  (* Noah's Ark: remove earlier identical elements (up to 3) *)
  let rec count_and_remove same acc = function
    | [] -> List.rev acc
    | Marker :: rest -> List.rev acc @ (Marker :: rest)
    | Entry e :: rest when e.name = name && e.attrs = attrs ->
      if same >= 2 then
        count_and_remove same acc rest  (* Remove this one *)
      else
        count_and_remove (same + 1) (Entry e :: acc) rest
    | x :: rest -> count_and_remove same (x :: acc) rest
  in
  t.active_formatting <- count_and_remove 0 [] t.active_formatting;
  t.active_formatting <- Entry { name; attrs; node } :: t.active_formatting

let clear_active_formatting_to_marker t =
  let rec loop = function
    | [] -> []
    | Marker :: rest -> rest
    | _ :: rest -> loop rest
  in
  t.active_formatting <- loop t.active_formatting

let reconstruct_active_formatting t =
  let rec find_to_reconstruct acc = function
    | [] -> acc
    | Marker :: _ -> acc
    | Entry e :: rest ->
      if List.exists (fun n -> n == e.node) t.open_elements then acc
      else find_to_reconstruct (Entry e :: acc) rest
  in
  let to_reconstruct = find_to_reconstruct [] t.active_formatting in
  List.iter (fun entry ->
    match entry with
    | Entry e ->
      let node = insert_element t e.name e.attrs in
      t.open_elements <- node :: t.open_elements;
      (* Update the entry to point to new node *)
      t.active_formatting <- List.map (fun x ->
        if x == entry then Entry { e with node }
        else x
      ) t.active_formatting
    | Marker -> ()
  ) to_reconstruct

(* Adoption agency algorithm - follows WHATWG spec *)
let adoption_agency t tag_name =
  (* Step 1: If current node is subject and not in active formatting list, just pop *)
  (match current_node t with
   | Some n when n.Dom.name = tag_name ->
     let in_active = List.exists (function
       | Entry e -> e.name = tag_name
       | Marker -> false
     ) t.active_formatting in
     if not in_active then begin
       pop_current t;
       () (* Return early - this case is handled *)
     end
   | _ -> ());

  (* Step 2: Outer loop *)
  let outer_loop_counter = ref 0 in
  let done_flag = ref false in

  while !outer_loop_counter < 8 && not !done_flag do
    incr outer_loop_counter;

    (* Step 3: Find formatting element in active formatting list *)
    let rec find_formatting_index idx = function
      | [] -> None
      | Marker :: _ -> None
      | Entry e :: rest ->
        if e.name = tag_name then Some (idx, e.node, e.attrs)
        else find_formatting_index (idx + 1) rest
    in
    let formatting_entry = find_formatting_index 0 t.active_formatting in

    match formatting_entry with
    | None ->
      (* No formatting element found - done *)
      done_flag := true
    | Some (fmt_idx, fmt_node, fmt_attrs) ->

      (* Step 4: Check if formatting element is in open elements *)
      if not (List.exists (fun n -> n == fmt_node) t.open_elements) then begin
        parse_error t "adoption-agency-1.2";
        t.active_formatting <- List.filteri (fun i _ -> i <> fmt_idx) t.active_formatting;
        done_flag := true
      end
      (* Step 5: Check if formatting element is in scope *)
      else if not (has_element_in_scope t tag_name) then begin
        parse_error t "adoption-agency-1.3";
        done_flag := true
      end else begin
        (* Step 6: Parse error if not current node *)
        (match current_node t with
         | Some n when n != fmt_node -> parse_error t "adoption-agency-1.3"
         | _ -> ());

        (* Step 7: Find furthest block - first special element BELOW formatting element *)
        (* open_elements is [current(top)...html(bottom)], formatting element is somewhere in the middle *)
        (* We need the first special element going from formatting element toward current *)
        (* This is the "topmost" (closest to formatting element) special element that is "lower" (closer to current) *)
        let fmt_stack_idx = ref (-1) in
        List.iteri (fun i n -> if n == fmt_node then fmt_stack_idx := i) t.open_elements;
        let furthest_block =
          if !fmt_stack_idx <= 0 then None
          else begin
            (* Look from fmt_stack_idx-1 down to 0, find first special element *)
            let rec find_from_idx idx =
              if idx < 0 then None
              else
                let n = List.nth t.open_elements idx in
                if is_special_element n then Some n
                else find_from_idx (idx - 1)
            in
            find_from_idx (!fmt_stack_idx - 1)
          end
        in

        match furthest_block with
        | None ->
          (* Step 8: No furthest block - pop elements including formatting element *)
          pop_until t (fun n -> n == fmt_node);
          t.active_formatting <- List.filteri (fun i _ -> i <> fmt_idx) t.active_formatting;
          done_flag := true

        | Some fb ->
          (* Step 9: Let common ancestor be element immediately above formatting element *)
          let rec find_common_ancestor = function
            | [] -> None
            | n :: rest when n == fmt_node ->
              (match rest with x :: _ -> Some x | [] -> None)
            | _ :: rest -> find_common_ancestor rest
          in
          let common_ancestor = find_common_ancestor t.open_elements in

          (* Step 10: Bookmark starts after formatting element *)
          let bookmark = ref (fmt_idx + 1) in

          (* Step 11: Let last_node = furthest block *)
          let last_node = ref fb in

          (* Step 12: Inner loop *)
          (* The inner loop processes elements between furthest_block and formatting_element,
             removing non-formatting elements and reparenting formatting elements *)
          let inner_loop_counter = ref 0 in

          (* Get index of furthest block in open elements *)
          let fb_idx = ref 0 in
          List.iteri (fun i n -> if n == fb then fb_idx := i) t.open_elements;

          (* Start from element after furthest block (toward formatting element) *)
          let node_idx = ref (!fb_idx + 1) in

          while !node_idx < List.length t.open_elements &&
                (List.nth t.open_elements !node_idx) != fmt_node do
            incr inner_loop_counter;
            let current_node = List.nth t.open_elements !node_idx in

            (* Step 12.3: Find node in active formatting list *)
            let rec find_node_in_formatting idx = function
              | [] -> None
              | Entry e :: _rest when e.node == current_node -> Some idx
              | _ :: rest -> find_node_in_formatting (idx + 1) rest
            in
            let node_fmt_idx = find_node_in_formatting 0 t.active_formatting in

            (* Step 12.4: If inner loop counter > 3 and node in active formatting, remove it *)
            let node_fmt_idx =
              match node_fmt_idx with
              | Some idx when !inner_loop_counter > 3 ->
                t.active_formatting <- List.filteri (fun i _ -> i <> idx) t.active_formatting;
                if idx < !bookmark then decr bookmark;
                None
              | x -> x
            in

            (* Step 12.5: If node not in active formatting, remove from stack and continue *)
            match node_fmt_idx with
            | None ->
              (* Remove from stack - this shifts indices *)
              t.open_elements <- List.filteri (fun i _ -> i <> !node_idx) t.open_elements
              (* Don't increment node_idx since we removed an element *)

            | Some af_idx ->
              (* Step 12.6: Create new element for node *)
              let (node_name, node_attrs) = match List.nth t.active_formatting af_idx with
                | Entry e -> (e.name, e.attrs)
                | Marker -> failwith "unexpected marker"
              in
              let new_node_elem = Dom.create_element node_name ~attrs:node_attrs () in

              (* Update active formatting with new node *)
              t.active_formatting <- List.mapi (fun i entry ->
                if i = af_idx then Entry { name = node_name; node = new_node_elem; attrs = node_attrs }
                else entry
              ) t.active_formatting;

              (* Replace node in open elements *)
              t.open_elements <- List.mapi (fun i n ->
                if i = !node_idx then new_node_elem else n
              ) t.open_elements;

              (* Step 12.7: If last_node is furthest block, update bookmark *)
              if !last_node == fb then
                bookmark := af_idx + 1;

              (* Step 12.8: Reparent last_node to new node *)
              (match !last_node.Dom.parent with
               | Some p -> Dom.remove_child p !last_node
               | None -> ());
              Dom.append_child new_node_elem !last_node;

              (* Step 12.9: Let last_node = new node *)
              last_node := new_node_elem;

              (* Move to next element *)
              incr node_idx
          done;

          (* Step 13: Insert last_node into common ancestor *)
          (match common_ancestor with
           | Some ca ->
             (match !last_node.Dom.parent with
              | Some p -> Dom.remove_child p !last_node
              | None -> ());
             (* Check if we need foster parenting *)
             if t.foster_parenting && Parser_constants.is_foster_parenting_element ca.Dom.name then begin
               (* Find table and insert before it *)
               let rec find_table = function
                 | [] -> None
                 | n :: rest when n.Dom.name = "table" -> Some (n, rest)
                 | _ :: rest -> find_table rest
               in
               match find_table t.open_elements with
               | Some (table, _) ->
                 (match table.Dom.parent with
                  | Some parent -> Dom.insert_before parent !last_node table
                  | None -> Dom.append_child ca !last_node)
               | None -> Dom.append_child ca !last_node
             end else begin
               (* If common ancestor is template, insert into its content *)
               match ca.Dom.template_content with
               | Some tc -> Dom.append_child tc !last_node
               | None -> Dom.append_child ca !last_node
             end
           | None -> ());

          (* Step 14: Create new formatting element *)
          let new_formatting = Dom.create_element tag_name ~attrs:fmt_attrs () in

          (* Step 15: Move children of furthest block to new formatting element *)
          let fb_children = fb.Dom.children in
          List.iter (fun child ->
            Dom.remove_child fb child;
            Dom.append_child new_formatting child
          ) fb_children;

          (* Step 16: Append new formatting element to furthest block *)
          Dom.append_child fb new_formatting;

          (* Step 17: Remove old from active formatting, insert new at bookmark *)
          let new_entry = Entry { name = tag_name; node = new_formatting; attrs = fmt_attrs } in
          t.active_formatting <- List.filteri (fun i _ -> i <> fmt_idx) t.active_formatting;
          (* Adjust bookmark since we removed an element *)
          let adjusted_bookmark = if fmt_idx < !bookmark then !bookmark - 1 else !bookmark in
          let rec insert_at_bookmark idx acc = function
            | [] -> List.rev (new_entry :: acc)
            | x :: rest when idx = adjusted_bookmark ->
              List.rev_append acc (new_entry :: x :: rest)
            | x :: rest -> insert_at_bookmark (idx + 1) (x :: acc) rest
          in
          t.active_formatting <- insert_at_bookmark 0 [] t.active_formatting;

          (* Step 18: Remove formatting element from open elements, insert new after furthest block *)
          (* "After" in stack terms means new_formatting should be between fb and current node *)
          (* In our list orientation (current at index 0), this means new_formatting at lower index than fb *)
          t.open_elements <- List.filter (fun n -> n != fmt_node) t.open_elements;
          (* Find fb and insert new_formatting before it (lower index = closer to current) *)
          let rec insert_before acc = function
            | [] -> List.rev (new_formatting :: acc)
            | n :: rest when n == fb ->
              (* Insert new_formatting before fb: acc reversed, then new_formatting, then fb, then rest *)
              List.rev_append acc (new_formatting :: n :: rest)
            | n :: rest -> insert_before (n :: acc) rest
          in
          t.open_elements <- insert_before [] t.open_elements
          (* Continue outer loop *)
      end
  done

(* Close p element *)
let close_p_element t =
  generate_implied_end_tags t ~except:"p" ();
  (match current_node t with
   | Some n when n.Dom.name <> "p" -> parse_error t "end-tag-p-implied-but-open-elements"
   | _ -> ());
  pop_until_tag t "p"

(* Reset insertion mode *)
let reset_insertion_mode t =
  let rec check_node last = function
    | [] -> t.mode <- Parser_insertion_mode.In_body
    | node :: rest ->
      let is_last = rest = [] in
      let node_to_check =
        if is_last then
          match t.fragment_context with
          | Some ctx -> Dom.create_element ctx.tag_name ~namespace:ctx.namespace ()
          | None -> node
        else node
      in
      let name = node_to_check.Dom.name in
      if name = "select" then begin
        if not is_last then begin
          let rec find_table_or_template = function
            | [] -> ()
            | n :: rest ->
              if n.Dom.name = "template" then t.mode <- Parser_insertion_mode.In_select
              else if n.Dom.name = "table" then t.mode <- Parser_insertion_mode.In_select_in_table
              else find_table_or_template rest
          in
          find_table_or_template rest
        end;
        if t.mode <> Parser_insertion_mode.In_select_in_table then
          t.mode <- Parser_insertion_mode.In_select
      end else if Parser_constants.is_table_cell_element name && not is_last then
        t.mode <- Parser_insertion_mode.In_cell
      else if name = "tr" then
        t.mode <- Parser_insertion_mode.In_row
      else if Parser_constants.is_table_section_element name then
        t.mode <- Parser_insertion_mode.In_table_body
      else if name = "caption" then
        t.mode <- Parser_insertion_mode.In_caption
      else if name = "colgroup" then
        t.mode <- Parser_insertion_mode.In_column_group
      else if name = "table" then
        t.mode <- Parser_insertion_mode.In_table
      else if name = "template" then
        t.mode <- (match t.template_modes with m :: _ -> m | [] -> Parser_insertion_mode.In_template)
      else if name = "head" && not is_last then
        t.mode <- Parser_insertion_mode.In_head
      else if name = "body" then
        t.mode <- Parser_insertion_mode.In_body
      else if name = "frameset" then
        t.mode <- Parser_insertion_mode.In_frameset
      else if name = "html" then
        t.mode <- (if t.head_element = None then Parser_insertion_mode.Before_head else Parser_insertion_mode.After_head)
      else if is_last then
        t.mode <- Parser_insertion_mode.In_body
      else
        check_node last rest
  in
  check_node false t.open_elements

let is_whitespace s =
  let ws = [' '; '\t'; '\n'; '\x0C'; '\r'] in
  String.for_all (fun c -> List.mem c ws) s

(* Mode handlers *)
let rec process_initial t token =
  match token with
  | Token.Character data when is_whitespace data -> ()
  | Token.Comment data -> insert_comment_to_document t data
  | Token.Doctype dt ->
    let location = Dom.make_location ~line:t.current_line ~column:t.current_column () in
    let node = Dom.create_doctype ?name:dt.name ?public_id:dt.public_id ?system_id:dt.system_id ~location () in
    Dom.append_child t.document node;
    (* Quirks mode detection *)
    if dt.force_quirks then
      t.quirks_mode <- Dom.Quirks
    else if dt.name <> Some "html" then
      t.quirks_mode <- Dom.Quirks
    else begin
      let pub = Option.map String.lowercase_ascii dt.public_id in
      let sys = Option.map String.lowercase_ascii dt.system_id in
      let is_quirky =
        (match pub with
         | Some p -> List.mem p Parser_constants.quirky_public_matches ||
                     List.exists (fun prefix -> String.length p >= String.length prefix &&
                                                String.sub p 0 (String.length prefix) = prefix) Parser_constants.quirky_public_prefixes
         | None -> false) ||
        (match sys with
         | Some s -> List.mem s Parser_constants.quirky_system_matches
         | None -> false)
      in
      if is_quirky then t.quirks_mode <- Dom.Quirks
      else begin
        let is_limited_quirky =
          match pub with
          | Some p -> List.exists (fun prefix -> String.length p >= String.length prefix &&
                                                  String.sub p 0 (String.length prefix) = prefix)
                        Parser_constants.limited_quirky_public_prefixes
          | None -> false
        in
        if is_limited_quirky then t.quirks_mode <- Dom.Limited_quirks
      end
    end;
    t.mode <- Parser_insertion_mode.Before_html
  | _ ->
    parse_error t "expected-doctype-but-got-other";
    t.quirks_mode <- Dom.Quirks;
    t.mode <- Parser_insertion_mode.Before_html;
    process_token t token

and process_before_html t token =
  match token with
  | Token.Doctype _ -> parse_error t "unexpected-doctype"
  | Token.Comment data -> insert_comment_to_document t data
  | Token.Character data when is_whitespace data -> ()
  | Token.Tag { kind = Token.Start; name = "html"; attrs; _ } ->
    let html = insert_element t "html" attrs in
    t.open_elements <- [html];
    t.mode <- Parser_insertion_mode.Before_head
  | Token.Tag { kind = Token.End; name; _ } when List.mem name ["head"; "body"; "html"; "br"] ->
    let html = insert_element t "html" [] in
    t.open_elements <- [html];
    t.mode <- Parser_insertion_mode.Before_head;
    process_token t token
  | Token.Tag { kind = Token.End; name; _ } ->
    parse_error t ("unexpected-end-tag:" ^ name)
  | _ ->
    let html = insert_element t "html" [] in
    t.open_elements <- [html];
    t.mode <- Parser_insertion_mode.Before_head;
    process_token t token

and process_before_head t token =
  match token with
  | Token.Character data when is_whitespace data -> ()
  | Token.Comment data -> insert_comment t data
  | Token.Doctype _ -> parse_error t "unexpected-doctype"
  | Token.Tag { kind = Token.Start; name = "html"; _ } ->
    process_in_body t token
  | Token.Tag { kind = Token.Start; name = "head"; attrs; _ } ->
    let head = insert_element t "head" attrs in
    t.open_elements <- head :: t.open_elements;
    t.head_element <- Some head;
    t.mode <- Parser_insertion_mode.In_head
  | Token.Tag { kind = Token.End; name; _ } when List.mem name ["head"; "body"; "html"; "br"] ->
    let head = insert_element t "head" [] in
    t.open_elements <- head :: t.open_elements;
    t.head_element <- Some head;
    t.mode <- Parser_insertion_mode.In_head;
    process_token t token
  | Token.Tag { kind = Token.End; name; _ } ->
    parse_error t ("unexpected-end-tag:" ^ name)
  | _ ->
    let head = insert_element t "head" [] in
    t.open_elements <- head :: t.open_elements;
    t.head_element <- Some head;
    t.mode <- Parser_insertion_mode.In_head;
    process_token t token

and process_in_head t token =
  match token with
  | Token.Character data when is_whitespace data ->
    insert_character t data
  | Token.Character data ->
    (* Extract leading whitespace *)
    let rec count_leading_ws i =
      if i >= String.length data then i
      else match data.[i] with
        | '\t' | '\n' | '\x0C' | '\r' | ' ' -> count_leading_ws (i + 1)
        | _ -> i
    in
    let ws_count = count_leading_ws 0 in
    let leading_ws = String.sub data 0 ws_count in
    let remaining = String.sub data ws_count (String.length data - ws_count) in
    (* If there's leading whitespace and current element has children, insert it *)
    if leading_ws <> "" then
      (match current_node t with
       | Some n when n.Dom.children <> [] -> insert_character t leading_ws
       | _ -> ());
    pop_current t;
    t.mode <- Parser_insertion_mode.After_head;
    process_token t (Token.Character remaining)
  | Token.Comment data ->
    insert_comment t data
  | Token.Doctype _ ->
    parse_error t "unexpected-doctype"
  | Token.Tag { kind = Token.Start; name = "html"; _ } ->
    process_in_body t token
  | Token.Tag { kind = Token.Start; name; attrs; _ }
    when List.mem name ["base"; "basefont"; "bgsound"; "link"; "meta"] ->
    ignore (insert_element t name attrs)
  | Token.Tag { kind = Token.Start; name = "title"; attrs; self_closing } ->
    ignore (insert_element_for_token t { kind = Token.Start; name = "title"; attrs; self_closing });
    t.original_mode <- Some t.mode;
    t.mode <- Parser_insertion_mode.Text
  | Token.Tag { kind = Token.Start; name; attrs; self_closing }
    when List.mem name ["noframes"; "style"] ->
    ignore (insert_element_for_token t { kind = Token.Start; name; attrs; self_closing });
    t.original_mode <- Some t.mode;
    t.mode <- Parser_insertion_mode.Text
  | Token.Tag { kind = Token.Start; name = "noscript"; attrs; self_closing } ->
    (* Scripting is disabled: parse noscript content as HTML *)
    ignore (insert_element_for_token t { kind = Token.Start; name = "noscript"; attrs; self_closing });
    t.mode <- Parser_insertion_mode.In_head_noscript
  | Token.Tag { kind = Token.Start; name = "script"; attrs; self_closing } ->
    ignore (insert_element_for_token t { kind = Token.Start; name = "script"; attrs; self_closing });
    t.original_mode <- Some t.mode;
    t.mode <- Parser_insertion_mode.Text
  | Token.Tag { kind = Token.End; name = "head"; _ } ->
    pop_current t;
    t.mode <- Parser_insertion_mode.After_head
  | Token.Tag { kind = Token.End; name; _ } when List.mem name ["body"; "html"; "br"] ->
    pop_current t;
    t.mode <- Parser_insertion_mode.After_head;
    process_token t token
  | Token.Tag { kind = Token.Start; name = "template"; attrs; _ } ->
    let node = Dom.create_template ~attrs () in
    let (parent, _) = appropriate_insertion_place t in
    Dom.append_child parent node;
    t.open_elements <- node :: t.open_elements;
    push_formatting_marker t;
    t.frameset_ok <- false;
    t.mode <- Parser_insertion_mode.In_template;
    t.template_modes <- Parser_insertion_mode.In_template :: t.template_modes
  | Token.Tag { kind = Token.End; name = "template"; _ } ->
    if not (List.exists (fun n -> n.Dom.name = "template" && is_in_html_namespace n) t.open_elements) then
      parse_error t "unexpected-end-tag"
    else begin
      generate_all_implied_end_tags t;
      (match current_node t with
       | Some n when not (n.Dom.name = "template" && is_in_html_namespace n) -> parse_error t "unexpected-end-tag"
       | _ -> ());
      pop_until_html_tag t "template";
      clear_active_formatting_to_marker t;
      t.template_modes <- (match t.template_modes with _ :: rest -> rest | [] -> []);
      reset_insertion_mode t
    end
  | Token.Tag { kind = Token.Start; name = "head"; _ } ->
    parse_error t "unexpected-start-tag"
  | Token.Tag { kind = Token.End; name; _ } ->
    parse_error t ("unexpected-end-tag:" ^ name)
  | _ ->
    pop_current t;
    t.mode <- Parser_insertion_mode.After_head;
    process_token t token

and process_in_head_noscript t token =
  match token with
  | Token.Character data when is_whitespace data ->
    process_in_head t token
  | Token.Character _ ->
    parse_error t "unexpected-char-in-noscript";
    pop_current t;  (* Pop noscript *)
    t.mode <- Parser_insertion_mode.In_head;
    process_token t token
  | Token.Comment _ ->
    process_in_head t token
  | Token.Doctype _ ->
    parse_error t "unexpected-doctype"
  | Token.Tag { kind = Token.Start; name = "html"; _ } ->
    process_in_body t token
  | Token.Tag { kind = Token.Start; name; _ }
    when List.mem name ["basefont"; "bgsound"; "link"; "meta"; "noframes"; "style"] ->
    process_in_head t token
  | Token.Tag { kind = Token.Start; name; _ }
    when List.mem name ["head"; "noscript"] ->
    parse_error t "unexpected-start-tag"
  | Token.Tag { kind = Token.Start; name; _ } ->
    parse_error t ("bad-start-tag-in-head-noscript:" ^ name);
    pop_current t;  (* Pop noscript *)
    t.mode <- Parser_insertion_mode.In_head;
    process_token t token
  | Token.Tag { kind = Token.End; name = "noscript"; _ } ->
    pop_current t;  (* Pop noscript *)
    t.mode <- Parser_insertion_mode.In_head
  | Token.Tag { kind = Token.End; name = "br"; _ } ->
    parse_error t "unexpected-end-tag";
    pop_current t;  (* Pop noscript *)
    t.mode <- Parser_insertion_mode.In_head;
    process_token t token
  | Token.Tag { kind = Token.End; name; _ } ->
    parse_error t ("unexpected-end-tag:" ^ name)
  | Token.EOF ->
    parse_error t "expected-closing-tag-but-got-eof";
    pop_current t;  (* Pop noscript *)
    t.mode <- Parser_insertion_mode.In_head;
    process_token t token

and process_after_head t token =
  match token with
  | Token.Character data when is_whitespace data ->
    insert_character t data
  | Token.Comment data ->
    insert_comment t data
  | Token.Doctype _ ->
    parse_error t "unexpected-doctype"
  | Token.Tag { kind = Token.Start; name = "html"; _ } ->
    process_in_body t token
  | Token.Tag { kind = Token.Start; name = "body"; attrs; _ } ->
    ignore (insert_element t "body" ~push:true attrs);
    t.frameset_ok <- false;
    t.mode <- Parser_insertion_mode.In_body
  | Token.Tag { kind = Token.Start; name = "frameset"; attrs; _ } ->
    ignore (insert_element t "frameset" ~push:true attrs);
    t.mode <- Parser_insertion_mode.In_frameset
  | Token.Tag { kind = Token.Start; name = "input"; attrs; _ } ->
    (* Special handling for input type="hidden" - parse error, ignore *)
    let input_type = List.assoc_opt "type" attrs in
    (match input_type with
     | Some typ when String.lowercase_ascii typ = "hidden" ->
       parse_error t "unexpected-hidden-input-after-head"
     | _ ->
       (* Non-hidden input creates body *)
       let body = insert_element t "body" [] in
       t.open_elements <- body :: t.open_elements;
       t.mode <- Parser_insertion_mode.In_body;
       process_token t token)
  | Token.Tag { kind = Token.Start; name; _ }
    when List.mem name ["base"; "basefont"; "bgsound"; "link"; "meta"; "noframes"; "script"; "style"; "template"; "title"] ->
    parse_error t "unexpected-start-tag";
    (match t.head_element with
     | Some head ->
       t.open_elements <- head :: t.open_elements;
       process_in_head t token;
       t.open_elements <- List.filter (fun n -> n != head) t.open_elements
     | None -> ())
  | Token.Tag { kind = Token.End; name = "template"; _ } ->
    process_in_head t token
  | Token.Tag { kind = Token.End; name; _ } when List.mem name ["body"; "html"; "br"] ->
    let body = insert_element t "body" [] in
    t.open_elements <- body :: t.open_elements;
    t.mode <- Parser_insertion_mode.In_body;
    process_token t token
  | Token.Tag { kind = Token.Start; name = "head"; _ } ->
    parse_error t "unexpected-start-tag"
  | Token.Tag { kind = Token.End; name; _ } ->
    parse_error t ("unexpected-end-tag:" ^ name)
  | _ ->
    let body = insert_element t "body" [] in
    t.open_elements <- body :: t.open_elements;
    t.mode <- Parser_insertion_mode.In_body;
    process_token t token

and process_in_body t token =
  match token with
  | Token.Character "\x00" ->
    parse_error t "unexpected-null-character"
  | Token.Character data ->
    reconstruct_active_formatting t;
    insert_character t data;
    if not (is_whitespace data) then t.frameset_ok <- false
  | Token.Comment data ->
    insert_comment t data
  | Token.Doctype _ ->
    parse_error t "unexpected-doctype"
  | Token.Tag { kind = Token.Start; name = "html"; attrs; _ } ->
    parse_error t "unexpected-start-tag";
    if not (List.exists (fun n -> n.Dom.name = "template") t.open_elements) then
      (* Find the html element (at the bottom of the stack) *)
      let html_elem = List.find_opt (fun n -> n.Dom.name = "html") t.open_elements in
      (match html_elem with
      | Some html ->
        List.iter (fun (k, v) ->
          if not (Dom.has_attr html k) then Dom.set_attr html k v
        ) attrs
      | None -> ())
  | Token.Tag { kind = Token.Start; name; _ }
    when List.mem name ["base"; "basefont"; "bgsound"; "link"; "meta"; "noframes"; "script"; "style"; "template"; "title"] ->
    process_in_head t token
  | Token.Tag { kind = Token.End; name = "template"; _ } ->
    process_in_head t token
  | Token.Tag { kind = Token.Start; name = "body"; attrs; _ } ->
    parse_error t "unexpected-start-tag";
    (* Find body element on stack - it should be near the end (html is last) *)
    let body = List.find_opt (fun n -> n.Dom.name = "body") t.open_elements in
    (match body with
     | Some body when not (List.exists (fun n -> n.Dom.name = "template") t.open_elements) ->
       t.frameset_ok <- false;
       List.iter (fun (k, v) ->
         if not (Dom.has_attr body k) then Dom.set_attr body k v
       ) attrs
     | _ -> ())
  | Token.Tag { kind = Token.Start; name = "frameset"; attrs; _ } ->
    if not t.frameset_ok then
      parse_error t "unexpected-start-tag-ignored"
    else begin
      (* Find body element on the stack *)
      let rec find_body_index idx = function
        | [] -> None
        | n :: rest ->
          if n.Dom.name = "body" then Some (idx, n)
          else find_body_index (idx + 1) rest
      in
      match find_body_index 0 t.open_elements with
      | None ->
        parse_error t "unexpected-start-tag-ignored"
      | Some (idx, body_elem) ->
        (* Remove body from its parent (the html element) *)
        (match body_elem.Dom.parent with
         | Some parent -> Dom.remove_child parent body_elem
         | None -> ());
        (* Pop all elements up to and including body - keep only elements after body_idx *)
        let rec drop n lst = if n <= 0 then lst else match lst with [] -> [] | _ :: rest -> drop (n - 1) rest in
        t.open_elements <- drop (idx + 1) t.open_elements;
        (* Insert frameset element *)
        ignore (insert_element t "frameset" ~push:true attrs);
        t.mode <- Parser_insertion_mode.In_frameset
    end
  | Token.EOF ->
    if t.template_modes <> [] then
      process_in_template t token
    else begin
      let has_unclosed = List.exists (fun n ->
        not (List.mem n.Dom.name ["dd"; "dt"; "li"; "optgroup"; "option"; "p"; "rb"; "rp"; "rt"; "rtc"; "tbody"; "td"; "tfoot"; "th"; "thead"; "tr"; "body"; "html"])
      ) t.open_elements in
      if has_unclosed then parse_error t "expected-closing-tag-but-got-eof"
    end
  | Token.Tag { kind = Token.End; name = "body"; _ } ->
    if not (has_element_in_scope t "body") then
      parse_error t "unexpected-end-tag"
    else begin
      let has_unclosed = List.exists (fun n ->
        not (List.mem n.Dom.name ["dd"; "dt"; "li"; "optgroup"; "option"; "p"; "rb"; "rp"; "rt"; "rtc"; "tbody"; "td"; "tfoot"; "th"; "thead"; "tr"; "body"; "html"])
      ) t.open_elements in
      if has_unclosed then parse_error t "end-tag-too-early";
      t.mode <- Parser_insertion_mode.After_body
    end
  | Token.Tag { kind = Token.End; name = "html"; _ } ->
    if not (has_element_in_scope t "body") then
      parse_error t "unexpected-end-tag"
    else begin
      t.mode <- Parser_insertion_mode.After_body;
      process_token t token
    end
  | Token.Tag { kind = Token.Start; name; attrs; _ }
    when List.mem name ["address"; "article"; "aside"; "blockquote"; "center"; "details"; "dialog"; "dir"; "div"; "dl"; "fieldset"; "figcaption"; "figure"; "footer"; "header"; "hgroup"; "main"; "menu"; "nav"; "ol"; "p"; "search"; "section"; "summary"; "ul"] ->
    if has_element_in_button_scope t "p" then close_p_element t;
    ignore (insert_element t name ~push:true attrs)
  | Token.Tag { kind = Token.Start; name; attrs; _ } when Parser_constants.is_heading_element name ->
    if has_element_in_button_scope t "p" then close_p_element t;
    (match current_node t with
     | Some n when Parser_constants.is_heading_element n.Dom.name ->
       parse_error t "unexpected-start-tag";
       pop_current t
     | _ -> ());
    ignore (insert_element t name ~push:true attrs)
  | Token.Tag { kind = Token.Start; name; attrs; _ } when List.mem name ["pre"; "listing"] ->
    if has_element_in_button_scope t "p" then close_p_element t;
    ignore (insert_element t name ~push:true attrs);
    t.ignore_lf <- true;
    t.frameset_ok <- false
  | Token.Tag { kind = Token.Start; name = "form"; attrs; _ } ->
    if t.form_element <> None && not (List.exists (fun n -> n.Dom.name = "template") t.open_elements) then
      parse_error t "unexpected-start-tag"
    else begin
      if has_element_in_button_scope t "p" then close_p_element t;
      let form = insert_element t "form" attrs in
      t.open_elements <- form :: t.open_elements;
      if not (List.exists (fun n -> n.Dom.name = "template") t.open_elements) then
        t.form_element <- Some form
    end
  | Token.Tag { kind = Token.Start; name = "li"; attrs; _ } ->
    t.frameset_ok <- false;
    let rec check = function
      | [] -> ()
      | n :: rest ->
        if n.Dom.name = "li" then begin
          generate_implied_end_tags t ~except:"li" ();
          (match current_node t with
           | Some cn when cn.Dom.name <> "li" -> parse_error t "unexpected-start-tag"
           | _ -> ());
          pop_until_tag t "li"
        end else if is_special_element n && not (List.mem (String.lowercase_ascii n.Dom.name) ["address"; "div"; "p"]) then
          ()
        else
          check rest
    in
    check t.open_elements;
    if has_element_in_button_scope t "p" then close_p_element t;
    ignore (insert_element t "li" ~push:true attrs)
  | Token.Tag { kind = Token.Start; name; attrs; _ } when List.mem name ["dd"; "dt"] ->
    t.frameset_ok <- false;
    let rec check = function
      | [] -> ()
      | n :: rest ->
        if List.mem n.Dom.name ["dd"; "dt"] then begin
          generate_implied_end_tags t ~except:n.Dom.name ();
          (match current_node t with
           | Some cn when cn.Dom.name <> n.Dom.name -> parse_error t "unexpected-start-tag"
           | _ -> ());
          pop_until_one_of t ["dd"; "dt"]
        end else if is_special_element n && not (List.mem (String.lowercase_ascii n.Dom.name) ["address"; "div"; "p"]) then
          ()
        else
          check rest
    in
    check t.open_elements;
    if has_element_in_button_scope t "p" then close_p_element t;
    ignore (insert_element t name ~push:true attrs)
  | Token.Tag { kind = Token.Start; name = "plaintext"; _ } ->
    if has_element_in_button_scope t "p" then close_p_element t;
    ignore (insert_element t "plaintext" ~push:true [])
    (* Tokenizer should switch to PLAINTEXT state *)
  | Token.Tag { kind = Token.Start; name = "button"; attrs; _ } ->
    if has_element_in_scope t "button" then begin
      parse_error t "unexpected-start-tag";
      generate_implied_end_tags t ();
      pop_until_tag t "button"
    end;
    reconstruct_active_formatting t;
    ignore (insert_element t "button" ~push:true attrs);
    t.frameset_ok <- false
  | Token.Tag { kind = Token.End; name; _ }
    when List.mem name ["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"] ->
    if not (has_element_in_scope t name) then
      parse_error t ("unexpected-end-tag:" ^ name)
    else begin
      generate_implied_end_tags t ();
      (match current_node t with
       | Some n when n.Dom.name <> name -> parse_error t "end-tag-too-early"
       | _ -> ());
      pop_until_tag t name
    end
  | Token.Tag { kind = Token.End; name = "form"; _ } ->
    if not (List.exists (fun n -> n.Dom.name = "template") t.open_elements) then begin
      let node = t.form_element in
      t.form_element <- None;
      match node with
      | None -> parse_error t "unexpected-end-tag"
      | Some form_node ->
        if not (has_element_in_scope t "form") then
          parse_error t "unexpected-end-tag"
        else begin
          generate_implied_end_tags t ();
          (match current_node t with
           | Some n when n != form_node -> parse_error t "end-tag-too-early"
           | _ -> ());
          t.open_elements <- List.filter (fun n -> n != form_node) t.open_elements
        end
    end else begin
      if not (has_element_in_scope t "form") then
        parse_error t "unexpected-end-tag"
      else begin
        generate_implied_end_tags t ();
        (match current_node t with
         | Some n when n.Dom.name <> "form" -> parse_error t "end-tag-too-early"
         | _ -> ());
        pop_until_tag t "form"
      end
    end
  | Token.Tag { kind = Token.End; name = "p"; _ } ->
    if not (has_element_in_button_scope t "p") then begin
      parse_error t "no-p-element-in-scope";
      ignore (insert_element t "p" ~push:true [])
    end;
    close_p_element t
  | Token.Tag { kind = Token.End; name = "li"; _ } ->
    if not (has_element_in_list_item_scope t "li") then
      parse_error t "unexpected-end-tag"
    else begin
      generate_implied_end_tags t ~except:"li" ();
      (match current_node t with
       | Some n when n.Dom.name <> "li" -> parse_error t "end-tag-too-early"
       | _ -> ());
      pop_until_tag t "li"
    end
  | Token.Tag { kind = Token.End; name; _ } when List.mem name ["dd"; "dt"] ->
    if not (has_element_in_scope t name) then
      parse_error t "unexpected-end-tag"
    else begin
      generate_implied_end_tags t ~except:name ();
      (match current_node t with
       | Some n when n.Dom.name <> name -> parse_error t "end-tag-too-early"
       | _ -> ());
      pop_until_tag t name
    end
  | Token.Tag { kind = Token.End; name; _ } when Parser_constants.is_heading_element name ->
    if not (has_element_in_scope_impl t Parser_constants.heading_elements Parser_constants.default_scope ~check_integration_points:true) then
      parse_error t "unexpected-end-tag"
    else begin
      generate_implied_end_tags t ();
      (match current_node t with
       | Some n when n.Dom.name <> name -> parse_error t "end-tag-too-early"
       | _ -> ());
      pop_until_one_of t Parser_constants.heading_elements
    end
  | Token.Tag { kind = Token.Start; name = "a"; attrs; _ } ->
    (* Check for existing <a> in active formatting *)
    let rec find_a = function
      | [] -> None
      | Marker :: _ -> None
      | Entry e :: _ when e.name = "a" -> Some e.node
      | _ :: rest -> find_a rest
    in
    (match find_a t.active_formatting with
     | Some existing ->
       parse_error t "unexpected-start-tag";
       adoption_agency t "a";
       t.active_formatting <- List.filter (function
         | Entry e -> e.node != existing
         | _ -> true
       ) t.active_formatting;
       t.open_elements <- List.filter (fun n -> n != existing) t.open_elements
     | None -> ());
    reconstruct_active_formatting t;
    let node = insert_element t "a" attrs in
    t.open_elements <- node :: t.open_elements;
    push_formatting_element t node "a" attrs
  | Token.Tag { kind = Token.Start; name; attrs; _ }
    when List.mem name ["b"; "big"; "code"; "em"; "font"; "i"; "s"; "small"; "strike"; "strong"; "tt"; "u"] ->
    reconstruct_active_formatting t;
    let node = insert_element t name attrs in
    t.open_elements <- node :: t.open_elements;
    push_formatting_element t node name attrs
  | Token.Tag { kind = Token.Start; name = "nobr"; attrs; _ } ->
    if has_element_in_scope t "nobr" then begin
      parse_error t "unexpected-start-tag";
      adoption_agency t "nobr";
      (* Remove nobr from active formatting *)
      t.active_formatting <- List.filter (function
        | Entry e -> e.name <> "nobr"
        | Marker -> true
      ) t.active_formatting;
      (* Remove nobr from open elements *)
      t.open_elements <- List.filter (fun n -> n.Dom.name <> "nobr") t.open_elements
    end;
    reconstruct_active_formatting t;
    let node = insert_element t "nobr" attrs in
    t.open_elements <- node :: t.open_elements;
    push_formatting_element t node "nobr" attrs
  | Token.Tag { kind = Token.End; name; _ }
    when List.mem name ["a"; "b"; "big"; "code"; "em"; "font"; "i"; "nobr"; "s"; "small"; "strike"; "strong"; "tt"; "u"] ->
    adoption_agency t name
  | Token.Tag { kind = Token.Start; name; attrs; _ }
    when List.mem name ["applet"; "marquee"; "object"] ->
    reconstruct_active_formatting t;
    ignore (insert_element t name ~push:true attrs);
    push_formatting_marker t;
    t.frameset_ok <- false
  | Token.Tag { kind = Token.End; name; _ }
    when List.mem name ["applet"; "marquee"; "object"] ->
    if not (has_element_in_scope t name) then
      parse_error t "unexpected-end-tag"
    else begin
      generate_implied_end_tags t ();
      (match current_node t with
       | Some n when n.Dom.name <> name -> parse_error t "end-tag-too-early"
       | _ -> ());
      pop_until_tag t name;
      clear_active_formatting_to_marker t
    end
  | Token.Tag { kind = Token.Start; name = "table"; attrs; _ } ->
    if t.quirks_mode <> Dom.Quirks && has_element_in_button_scope t "p" then
      close_p_element t;
    ignore (insert_element t "table" ~push:true attrs);
    t.frameset_ok <- false;
    t.mode <- Parser_insertion_mode.In_table
  | Token.Tag { kind = Token.End; name = "br"; _ } ->
    parse_error t "end-tag-br";
    reconstruct_active_formatting t;
    ignore (insert_element t "br" ~push:true []);
    pop_current t;
    t.frameset_ok <- false
  | Token.Tag { kind = Token.Start; name; attrs; _ }
    when List.mem name ["area"; "br"; "embed"; "img"; "keygen"; "wbr"] ->
    reconstruct_active_formatting t;
    ignore (insert_element t name ~push:true attrs);
    pop_current t;
    t.frameset_ok <- false
  | Token.Tag { kind = Token.Start; name = "input"; attrs; _ } ->
    reconstruct_active_formatting t;
    ignore (insert_element t "input" ~push:true attrs);
    pop_current t;
    let is_hidden = List.exists (fun (k, v) ->
      String.lowercase_ascii k = "type" && String.lowercase_ascii v = "hidden"
    ) attrs in
    if not is_hidden then t.frameset_ok <- false
  | Token.Tag { kind = Token.Start; name; attrs; _ }
    when List.mem name ["param"; "source"; "track"] ->
    ignore (insert_element_for_token t { kind = Token.Start; name; attrs; self_closing = false });
    pop_current t
  | Token.Tag { kind = Token.Start; name = "hr"; _ } ->
    if has_element_in_button_scope t "p" then close_p_element t;
    ignore (insert_element t "hr" ~push:true []);
    pop_current t;
    t.frameset_ok <- false
  | Token.Tag { kind = Token.Start; name = "image"; attrs; _ } ->
    parse_error t "unexpected-start-tag";
    (* Treat <image> as <img> *)
    reconstruct_active_formatting t;
    ignore (insert_element t "img" ~push:true attrs);
    pop_current t;
    t.frameset_ok <- false
  | Token.Tag { kind = Token.Start; name = "textarea"; attrs; _ } ->
    ignore (insert_element t "textarea" ~push:true attrs);
    t.ignore_lf <- true;
    t.original_mode <- Some t.mode;
    t.frameset_ok <- false;
    t.mode <- Parser_insertion_mode.Text
  | Token.Tag { kind = Token.Start; name = "xmp"; attrs; _ } ->
    if has_element_in_button_scope t "p" then close_p_element t;
    reconstruct_active_formatting t;
    t.frameset_ok <- false;
    ignore (insert_element_for_token t { kind = Token.Start; name = "xmp"; attrs; self_closing = false });
    t.original_mode <- Some t.mode;
    t.mode <- Parser_insertion_mode.Text
  | Token.Tag { kind = Token.Start; name = "iframe"; attrs; _ } ->
    t.frameset_ok <- false;
    ignore (insert_element_for_token t { kind = Token.Start; name = "iframe"; attrs; self_closing = false });
    t.original_mode <- Some t.mode;
    t.mode <- Parser_insertion_mode.Text
  | Token.Tag { kind = Token.Start; name = "noembed"; attrs; _ } ->
    ignore (insert_element_for_token t { kind = Token.Start; name = "noembed"; attrs; self_closing = false });
    t.original_mode <- Some t.mode;
    t.mode <- Parser_insertion_mode.Text
  | Token.Tag { kind = Token.Start; name = "select"; attrs; _ } ->
    reconstruct_active_formatting t;
    ignore (insert_element t "select" ~push:true attrs);
    t.frameset_ok <- false;
    if List.mem t.mode [Parser_insertion_mode.In_table; Parser_insertion_mode.In_caption; Parser_insertion_mode.In_table_body; Parser_insertion_mode.In_row; Parser_insertion_mode.In_cell] then
      t.mode <- Parser_insertion_mode.In_select_in_table
    else
      t.mode <- Parser_insertion_mode.In_select
  | Token.Tag { kind = Token.Start; name; attrs; _ } when List.mem name ["optgroup"; "option"] ->
    (match current_node t with
     | Some n when n.Dom.name = "option" -> pop_current t
     | _ -> ());
    reconstruct_active_formatting t;
    ignore (insert_element t name ~push:true attrs)
  | Token.Tag { kind = Token.Start; name; attrs; _ } when List.mem name ["rb"; "rtc"] ->
    if has_element_in_scope t "ruby" then begin
      generate_implied_end_tags t ()
    end;
    (match current_node t with
     | Some n when n.Dom.name <> "ruby" && n.Dom.name <> "rtc" -> parse_error t "unexpected-start-tag"
     | _ -> ());
    ignore (insert_element t name ~push:true attrs)
  | Token.Tag { kind = Token.Start; name; attrs; _ } when List.mem name ["rp"; "rt"] ->
    if has_element_in_scope t "ruby" then begin
      generate_implied_end_tags t ~except:"rtc" ()
    end;
    (match current_node t with
     | Some n when n.Dom.name <> "ruby" && n.Dom.name <> "rtc" -> parse_error t "unexpected-start-tag"
     | _ -> ());
    ignore (insert_element t name ~push:true attrs)
  | Token.Tag { kind = Token.Start; name = "math"; attrs; self_closing } ->
    reconstruct_active_formatting t;
    let adjusted_attrs = Parser_constants.adjust_mathml_attrs (Parser_constants.adjust_foreign_attrs attrs) in
    ignore (insert_foreign_element t { kind = Token.Start; name = "math"; attrs = adjusted_attrs; self_closing } (Some "mathml"));
    if self_closing then pop_current t
  | Token.Tag { kind = Token.Start; name = "svg"; attrs; self_closing } ->
    reconstruct_active_formatting t;
    let adjusted_attrs = Parser_constants.adjust_svg_attrs (Parser_constants.adjust_foreign_attrs attrs) in
    ignore (insert_foreign_element t { kind = Token.Start; name = "svg"; attrs = adjusted_attrs; self_closing } (Some "svg"));
    if self_closing then pop_current t
  | Token.Tag { kind = Token.Start; name; attrs; _ }
    when List.mem name ["col"; "frame"] ->
    (* In fragment context, insert these; otherwise ignore *)
    if t.fragment_context = None then
      parse_error t "unexpected-start-tag-ignored"
    else
      ignore (insert_element t name attrs)
  | Token.Tag { kind = Token.Start; name; _ }
    when List.mem name ["caption"; "colgroup"; "head"; "tbody"; "td"; "tfoot"; "th"; "thead"; "tr"] ->
    parse_error t "unexpected-start-tag"
  | Token.Tag { kind = Token.Start; name; attrs; self_closing } ->
    (* Any other start tag *)
    reconstruct_active_formatting t;
    ignore (insert_element t name ~push:true attrs);
    (* Check for self-closing on non-void HTML element *)
    if self_closing && not (Parser_constants.is_void_element name) then
      parse_error t "non-void-html-element-start-tag-with-trailing-solidus"
  | Token.Tag { kind = Token.End; name; _ } ->
    (* Any other end tag *)
    let rec check = function
      | [] -> ()
      | node :: rest ->
        if node.Dom.name = name then begin
          generate_implied_end_tags t ~except:name ();
          (match current_node t with
           | Some n when n.Dom.name <> name -> parse_error t "end-tag-too-early"
           | _ -> ());
          pop_until t (fun n -> n == node)
        end else if is_special_element node then
          parse_error t ("unexpected-end-tag:" ^ name)
        else
          check rest
    in
    check t.open_elements

and process_text t token =
  match token with
  | Token.Character data ->
    insert_character t data
  | Token.EOF ->
    parse_error t "expected-closing-tag-but-got-eof";
    pop_current t;
    t.mode <- Option.value t.original_mode ~default:Parser_insertion_mode.In_body;
    process_token t token
  | Token.Tag { kind = Token.End; _ } ->
    pop_current t;
    t.mode <- Option.value t.original_mode ~default:Parser_insertion_mode.In_body
  | _ -> ()

and process_in_table t token =
  match token with
  | Token.Character _ when (match current_node t with Some n -> Parser_constants.is_foster_parenting_element n.Dom.name | None -> false) ->
    t.pending_table_chars <- [];
    t.original_mode <- Some t.mode;
    t.mode <- Parser_insertion_mode.In_table_text;
    process_token t token
  | Token.Comment data ->
    insert_comment t data
  | Token.Doctype _ ->
    parse_error t "unexpected-doctype"
  | Token.Tag { kind = Token.Start; name = "caption"; attrs; _ } ->
    clear_stack_back_to_table_context t;
    push_formatting_marker t;
    ignore (insert_element t "caption" ~push:true attrs);
    t.mode <- Parser_insertion_mode.In_caption
  | Token.Tag { kind = Token.Start; name = "colgroup"; attrs; _ } ->
    clear_stack_back_to_table_context t;
    ignore (insert_element t "colgroup" ~push:true attrs);
    t.mode <- Parser_insertion_mode.In_column_group
  | Token.Tag { kind = Token.Start; name = "col"; _ } ->
    clear_stack_back_to_table_context t;
    ignore (insert_element t "colgroup" ~push:true []);
    t.mode <- Parser_insertion_mode.In_column_group;
    process_token t token
  | Token.Tag { kind = Token.Start; name; attrs; _ } when List.mem name ["tbody"; "tfoot"; "thead"] ->
    clear_stack_back_to_table_context t;
    ignore (insert_element t name ~push:true attrs);
    t.mode <- Parser_insertion_mode.In_table_body
  | Token.Tag { kind = Token.Start; name; _ } when List.mem name ["td"; "th"; "tr"] ->
    clear_stack_back_to_table_context t;
    ignore (insert_element t "tbody" ~push:true []);
    t.mode <- Parser_insertion_mode.In_table_body;
    process_token t token
  | Token.Tag { kind = Token.Start; name = "table"; _ } ->
    parse_error t "unexpected-start-tag";
    if has_element_in_table_scope t "table" then begin
      pop_until_tag t "table";
      reset_insertion_mode t;
      process_token t token
    end
  | Token.Tag { kind = Token.End; name = "table"; _ } ->
    if not (has_element_in_table_scope t "table") then
      parse_error t "unexpected-end-tag"
    else begin
      pop_until_tag t "table";
      reset_insertion_mode t
    end
  | Token.Tag { kind = Token.End; name; _ }
    when List.mem name ["body"; "caption"; "col"; "colgroup"; "html"; "tbody"; "td"; "tfoot"; "th"; "thead"; "tr"] ->
    parse_error t "unexpected-end-tag"
  | Token.Tag { kind = Token.Start; name; _ } when List.mem name ["style"; "script"; "template"] ->
    process_in_head t token
  | Token.Tag { kind = Token.End; name = "template"; _ } ->
    process_in_head t token
  | Token.Tag { kind = Token.Start; name = "input"; attrs; _ } ->
    let is_hidden = List.exists (fun (k, v) ->
      String.lowercase_ascii k = "type" && String.lowercase_ascii v = "hidden"
    ) attrs in
    if not is_hidden then begin
      parse_error t "start-tag-in-table:input";
      t.foster_parenting <- true;
      process_in_body t token;
      t.foster_parenting <- false
    end else begin
      parse_error t "start-tag-in-table:input";
      ignore (insert_element t "input" ~push:true attrs);
      pop_current t
    end
  | Token.Tag { kind = Token.Start; name = "form"; attrs; _ } ->
    parse_error t "unexpected-start-tag";
    if t.form_element = None && not (List.exists (fun n -> n.Dom.name = "template") t.open_elements) then begin
      let form = insert_element t "form" attrs in
      t.open_elements <- form :: t.open_elements;
      t.form_element <- Some form;
      pop_current t
    end
  | Token.EOF ->
    process_in_body t token
  | _ ->
    parse_error t "unexpected-token-in-table";
    t.foster_parenting <- true;
    process_in_body t token;
    t.foster_parenting <- false

and clear_stack_back_to_table_context t =
  let rec loop () =
    match current_node t with
    | Some n when not (List.mem n.Dom.name ["table"; "template"; "html"]) ->
      pop_current t;
      loop ()
    | _ -> ()
  in
  loop ()

and process_in_table_text t token =
  match token with
  | Token.Character data ->
    if String.contains data '\x00' then
      parse_error t "unexpected-null-character"
    else
      t.pending_table_chars <- data :: t.pending_table_chars
  | _ ->
    let pending = String.concat "" (List.rev t.pending_table_chars) in
    t.pending_table_chars <- [];
    if not (is_whitespace pending) then begin
      parse_error t "unexpected-character-in-table";
      t.foster_parenting <- true;
      reconstruct_active_formatting t;
      insert_character t pending;
      t.foster_parenting <- false
    end else
      insert_character t pending;
    t.mode <- Option.value t.original_mode ~default:Parser_insertion_mode.In_table;
    process_token t token

and process_in_caption t token =
  match token with
  | Token.Tag { kind = Token.End; name = "caption"; _ } ->
    if not (has_element_in_table_scope t "caption") then
      parse_error t "unexpected-end-tag"
    else begin
      generate_implied_end_tags t ();
      (match current_node t with
       | Some n when n.Dom.name <> "caption" -> parse_error t "end-tag-too-early"
       | _ -> ());
      pop_until_tag t "caption";
      clear_active_formatting_to_marker t;
      t.mode <- Parser_insertion_mode.In_table
    end
  | Token.Tag { kind = Token.Start; name; _ }
    when List.mem name ["caption"; "col"; "colgroup"; "tbody"; "td"; "tfoot"; "th"; "thead"; "tr"] ->
    if not (has_element_in_table_scope t "caption") then
      parse_error t "unexpected-start-tag"
    else begin
      generate_implied_end_tags t ();
      pop_until_tag t "caption";
      clear_active_formatting_to_marker t;
      t.mode <- Parser_insertion_mode.In_table;
      process_token t token
    end
  | Token.Tag { kind = Token.End; name = "table"; _ } ->
    if not (has_element_in_table_scope t "caption") then
      parse_error t "unexpected-end-tag"
    else begin
      generate_implied_end_tags t ();
      pop_until_tag t "caption";
      clear_active_formatting_to_marker t;
      t.mode <- Parser_insertion_mode.In_table;
      process_token t token
    end
  | Token.Tag { kind = Token.End; name; _ }
    when List.mem name ["body"; "col"; "colgroup"; "html"; "tbody"; "td"; "tfoot"; "th"; "thead"; "tr"] ->
    parse_error t "unexpected-end-tag"
  | _ ->
    process_in_body t token

and process_in_column_group t token =
  match token with
  | Token.Character data when is_whitespace data ->
    insert_character t data
  | Token.Character data ->
    (* Split leading whitespace from non-whitespace *)
    let ws_chars = [' '; '\t'; '\n'; '\x0C'; '\r'] in
    let len = String.length data in
    let ws_end = ref 0 in
    while !ws_end < len && List.mem data.[!ws_end] ws_chars do incr ws_end done;
    if !ws_end > 0 then
      insert_character t (String.sub data 0 !ws_end);
    if !ws_end < len then begin
      let remaining = String.sub data !ws_end (len - !ws_end) in
      (match current_node t with
       | Some n when n.Dom.name = "colgroup" ->
         pop_current t;
         t.mode <- Parser_insertion_mode.In_table;
         process_token t (Token.Character remaining)
       | _ ->
         parse_error t "unexpected-token")
    end
  | Token.Comment data ->
    insert_comment t data
  | Token.Doctype _ ->
    parse_error t "unexpected-doctype"
  | Token.Tag { kind = Token.Start; name = "html"; _ } ->
    process_in_body t token
  | Token.Tag { kind = Token.Start; name = "col"; attrs; _ } ->
    ignore (insert_element t "col" ~push:true attrs);
    pop_current t
  | Token.Tag { kind = Token.End; name = "colgroup"; _ } ->
    (match current_node t with
     | Some n when n.Dom.name <> "colgroup" -> parse_error t "unexpected-end-tag"
     | Some _ -> pop_current t; t.mode <- Parser_insertion_mode.In_table
     | None -> parse_error t "unexpected-end-tag")
  | Token.Tag { kind = Token.End; name = "col"; _ } ->
    parse_error t "unexpected-end-tag"
  | Token.Tag { kind = Token.Start; name = "template"; _ }
  | Token.Tag { kind = Token.End; name = "template"; _ } ->
    process_in_head t token
  | Token.EOF ->
    process_in_body t token
  | _ ->
    (match current_node t with
     | Some n when n.Dom.name = "colgroup" ->
       pop_current t;
       t.mode <- Parser_insertion_mode.In_table;
       process_token t token
     | _ ->
       parse_error t "unexpected-token")

and process_in_table_body t token =
  match token with
  | Token.Tag { kind = Token.Start; name = "tr"; attrs; _ } ->
    clear_stack_back_to_table_body_context t;
    ignore (insert_element t "tr" ~push:true attrs);
    t.mode <- Parser_insertion_mode.In_row
  | Token.Tag { kind = Token.Start; name; _ } when List.mem name ["th"; "td"] ->
    parse_error t "unexpected-start-tag";
    clear_stack_back_to_table_body_context t;
    ignore (insert_element t "tr" ~push:true []);
    t.mode <- Parser_insertion_mode.In_row;
    process_token t token
  | Token.Tag { kind = Token.End; name; _ } when List.mem name ["tbody"; "tfoot"; "thead"] ->
    if not (has_element_in_table_scope t name) then
      parse_error t "unexpected-end-tag"
    else begin
      clear_stack_back_to_table_body_context t;
      pop_current t;
      t.mode <- Parser_insertion_mode.In_table
    end
  | Token.Tag { kind = Token.Start; name; _ }
    when List.mem name ["caption"; "col"; "colgroup"; "tbody"; "tfoot"; "thead"] ->
    if not (has_element_in_scope_impl t ["tbody"; "tfoot"; "thead"] Parser_constants.table_scope ~check_integration_points:false) then
      parse_error t "unexpected-start-tag"
    else begin
      clear_stack_back_to_table_body_context t;
      pop_current t;
      t.mode <- Parser_insertion_mode.In_table;
      process_token t token
    end
  | Token.Tag { kind = Token.End; name = "table"; _ } ->
    if not (has_element_in_scope_impl t ["tbody"; "tfoot"; "thead"] Parser_constants.table_scope ~check_integration_points:false) then
      parse_error t "unexpected-end-tag"
    else begin
      clear_stack_back_to_table_body_context t;
      pop_current t;
      t.mode <- Parser_insertion_mode.In_table;
      process_token t token
    end
  | Token.Tag { kind = Token.End; name; _ }
    when List.mem name ["body"; "caption"; "col"; "colgroup"; "html"; "td"; "th"; "tr"] ->
    parse_error t "unexpected-end-tag"
  | _ ->
    process_in_table t token

and clear_stack_back_to_table_body_context t =
  let rec loop () =
    match current_node t with
    | Some n when not (List.mem n.Dom.name ["tbody"; "tfoot"; "thead"; "template"; "html"]) ->
      pop_current t;
      loop ()
    | _ -> ()
  in
  loop ()

and process_in_row t token =
  match token with
  | Token.Tag { kind = Token.Start; name; attrs; _ } when List.mem name ["th"; "td"] ->
    clear_stack_back_to_table_row_context t;
    ignore (insert_element t name ~push:true attrs);
    t.mode <- Parser_insertion_mode.In_cell;
    push_formatting_marker t
  | Token.Tag { kind = Token.End; name = "tr"; _ } ->
    if not (has_element_in_table_scope t "tr") then
      parse_error t "unexpected-end-tag"
    else begin
      clear_stack_back_to_table_row_context t;
      pop_current t;
      t.mode <- Parser_insertion_mode.In_table_body
    end
  | Token.Tag { kind = Token.Start; name; _ }
    when List.mem name ["caption"; "col"; "colgroup"; "tbody"; "tfoot"; "thead"; "tr"] ->
    if not (has_element_in_table_scope t "tr") then
      parse_error t "unexpected-start-tag"
    else begin
      clear_stack_back_to_table_row_context t;
      pop_current t;
      t.mode <- Parser_insertion_mode.In_table_body;
      process_token t token
    end
  | Token.Tag { kind = Token.End; name = "table"; _ } ->
    if not (has_element_in_table_scope t "tr") then
      parse_error t "unexpected-end-tag"
    else begin
      clear_stack_back_to_table_row_context t;
      pop_current t;
      t.mode <- Parser_insertion_mode.In_table_body;
      process_token t token
    end
  | Token.Tag { kind = Token.End; name; _ } when List.mem name ["tbody"; "tfoot"; "thead"] ->
    if not (has_element_in_table_scope t name) then
      parse_error t "unexpected-end-tag"
    else if not (has_element_in_table_scope t "tr") then
      parse_error t "unexpected-end-tag"
    else begin
      clear_stack_back_to_table_row_context t;
      pop_current t;
      t.mode <- Parser_insertion_mode.In_table_body;
      process_token t token
    end
  | Token.Tag { kind = Token.End; name; _ }
    when List.mem name ["body"; "caption"; "col"; "colgroup"; "html"; "td"; "th"] ->
    parse_error t "unexpected-end-tag"
  | _ ->
    process_in_table t token

and clear_stack_back_to_table_row_context t =
  let rec loop () =
    match current_node t with
    | Some n when not (List.mem n.Dom.name ["tr"; "template"; "html"]) ->
      pop_current t;
      loop ()
    | _ -> ()
  in
  loop ()

and process_in_cell t token =
  match token with
  | Token.Tag { kind = Token.End; name; _ } when Parser_constants.is_table_cell_element name ->
    if not (has_element_in_table_scope t name) then
      parse_error t "unexpected-end-tag"
    else begin
      generate_implied_end_tags t ();
      (match current_node t with
       | Some n when not (n.Dom.name = name && is_in_html_namespace n) -> parse_error t "end-tag-too-early"
       | _ -> ());
      pop_until_html_tag t name;
      clear_active_formatting_to_marker t;
      t.mode <- Parser_insertion_mode.In_row
    end
  | Token.Tag { kind = Token.Start; name; _ }
    when List.mem name ["caption"; "col"; "colgroup"; "tbody"; "td"; "tfoot"; "th"; "thead"; "tr"] ->
    if not (has_element_in_scope_impl t ["td"; "th"] Parser_constants.table_scope ~check_integration_points:false) then
      parse_error t "unexpected-start-tag"
    else begin
      close_cell t;
      process_token t token
    end
  | Token.Tag { kind = Token.End; name; _ }
    when List.mem name ["body"; "caption"; "col"; "colgroup"; "html"] ->
    parse_error t "unexpected-end-tag"
  | Token.Tag { kind = Token.End; name; _ }
    when Parser_constants.is_foster_parenting_element name ->
    if not (has_element_in_table_scope t name) then
      parse_error t "unexpected-end-tag"
    else begin
      close_cell t;
      process_token t token
    end
  | _ ->
    process_in_body t token

and close_cell t =
  generate_implied_end_tags t ();
  (match current_node t with
   | Some n when not (Parser_constants.is_table_cell_element n.Dom.name && is_in_html_namespace n) -> parse_error t "end-tag-too-early"
   | _ -> ());
  pop_until_html_one_of t ["td"; "th"];
  clear_active_formatting_to_marker t;
  t.mode <- Parser_insertion_mode.In_row

and process_in_select t token =
  match token with
  | Token.Character "\x00" ->
    parse_error t "unexpected-null-character"
  | Token.Character data ->
    reconstruct_active_formatting t;
    insert_character t data
  | Token.Comment data ->
    insert_comment t data
  | Token.Doctype _ ->
    parse_error t "unexpected-doctype"
  | Token.Tag { kind = Token.Start; name = "html"; _ } ->
    process_in_body t token
  | Token.Tag { kind = Token.Start; name = "option"; attrs; _ } ->
    (match current_node t with
     | Some n when n.Dom.name = "option" -> pop_current t
     | _ -> ());
    reconstruct_active_formatting t;
    ignore (insert_element t "option" ~push:true attrs)
  | Token.Tag { kind = Token.Start; name = "optgroup"; attrs; _ } ->
    (match current_node t with
     | Some n when n.Dom.name = "option" -> pop_current t
     | _ -> ());
    (match current_node t with
     | Some n when n.Dom.name = "optgroup" -> pop_current t
     | _ -> ());
    reconstruct_active_formatting t;
    ignore (insert_element t "optgroup" ~push:true attrs)
  | Token.Tag { kind = Token.Start; name = "hr"; _ } ->
    (match current_node t with
     | Some n when n.Dom.name = "option" -> pop_current t
     | _ -> ());
    (match current_node t with
     | Some n when n.Dom.name = "optgroup" -> pop_current t
     | _ -> ());
    ignore (insert_element t "hr" ~push:true []);
    pop_current t
  | Token.Tag { kind = Token.End; name = "optgroup"; _ } ->
    (match t.open_elements with
     | opt :: optg :: _ when opt.Dom.name = "option" && optg.Dom.name = "optgroup" ->
       pop_current t
     | _ -> ());
    (match current_node t with
     | Some n when n.Dom.name = "optgroup" -> pop_current t
     | _ -> parse_error t "unexpected-end-tag")
  | Token.Tag { kind = Token.End; name = "option"; _ } ->
    (match current_node t with
     | Some n when n.Dom.name = "option" -> pop_current t
     | _ -> parse_error t "unexpected-end-tag")
  | Token.Tag { kind = Token.End; name = "select"; _ } ->
    if not (has_element_in_select_scope t "select") then
      parse_error t "unexpected-end-tag"
    else begin
      pop_until_tag t "select";
      reset_insertion_mode t
    end
  | Token.Tag { kind = Token.Start; name = "select"; _ } ->
    parse_error t "unexpected-start-tag";
    (* Per spec: in IN_SELECT mode, select is always on the stack - just pop *)
    pop_until_tag t "select";
    reset_insertion_mode t
  | Token.Tag { kind = Token.Start; name; _ } when List.mem name ["input"; "textarea"] ->
    parse_error t "unexpected-start-tag";
    (* Per spec: in IN_SELECT mode, select is always on the stack - just pop *)
    pop_until_tag t "select";
    reset_insertion_mode t;
    process_token t token
  | Token.Tag { kind = Token.Start; name = "plaintext"; attrs; _ } ->
    (* plaintext is allowed in select - creates element, parser will switch tokenizer to PLAINTEXT mode *)
    reconstruct_active_formatting t;
    ignore (insert_element t "plaintext" ~push:true attrs)
  | Token.Tag { kind = Token.Start; name = "menuitem"; attrs; _ } ->
    (* menuitem is allowed in select *)
    reconstruct_active_formatting t;
    ignore (insert_element t "menuitem" ~push:true attrs)
  | Token.Tag { kind = Token.Start; name = "keygen"; attrs; _ } ->
    (* keygen is handled specially in select - inserted directly *)
    reconstruct_active_formatting t;
    ignore (insert_element t "keygen" attrs)
    (* Void element, don't push to stack *)
  | Token.Tag { kind = Token.Start; name = "svg"; attrs; self_closing } ->
    reconstruct_active_formatting t;
    let node = insert_foreign_element t { kind = Token.Start; name = "svg"; attrs; self_closing } (Some "svg") in
    if not self_closing then t.open_elements <- node :: t.open_elements
  | Token.Tag { kind = Token.Start; name = "math"; attrs; self_closing } ->
    reconstruct_active_formatting t;
    let node = insert_foreign_element t { kind = Token.Start; name = "math"; attrs; self_closing } (Some "mathml") in
    if not self_closing then t.open_elements <- node :: t.open_elements
  | Token.Tag { kind = Token.Start; name; _ } when List.mem name ["script"; "template"] ->
    process_in_head t token
  | Token.Tag { kind = Token.End; name = "template"; _ } ->
    process_in_head t token
  (* Allow certain HTML elements in select - newer spec behavior *)
  | Token.Tag { kind = Token.Start; name; attrs; self_closing } when List.mem name ["p"; "div"; "span"; "button"; "datalist"; "selectedcontent"] ->
    reconstruct_active_formatting t;
    let node = insert_element t name attrs in
    if not self_closing then t.open_elements <- node :: t.open_elements
  | Token.Tag { kind = Token.Start; name; attrs; _ } when List.mem name ["br"; "img"] ->
    reconstruct_active_formatting t;
    ignore (insert_element t name attrs)
    (* Don't push to stack - void elements *)
  (* Handle formatting elements in select *)
  | Token.Tag { kind = Token.Start; name; attrs; _ } when Parser_constants.is_formatting_element name ->
    reconstruct_active_formatting t;
    let node = insert_element t name ~push:true attrs in
    push_formatting_element t node name attrs
  | Token.Tag { kind = Token.End; name; _ } when Parser_constants.is_formatting_element name ->
    (* Find select element and check if formatting element is inside select *)
    let select_idx = ref None in
    let fmt_idx = ref None in
    List.iteri (fun i n ->
      if n.Dom.name = "select" && !select_idx = None then select_idx := Some i;
      if n.Dom.name = name then fmt_idx := Some i
    ) t.open_elements;
    (match !fmt_idx, !select_idx with
     | Some fi, Some si when fi < si ->
       (* Formatting element is inside select, run adoption agency *)
       adoption_agency t name
     | Some _, Some _ ->
       (* Formatting element is outside select boundary - parse error, ignore *)
       parse_error t "unexpected-end-tag"
     | Some _, None ->
       adoption_agency t name
     | None, _ ->
       parse_error t "unexpected-end-tag")
  (* End tags for HTML elements allowed in select *)
  | Token.Tag { kind = Token.End; name; _ } when List.mem name ["p"; "div"; "span"; "button"; "datalist"; "selectedcontent"] ->
    (* Find select and target indices *)
    let select_idx = ref None in
    let target_idx = ref None in
    List.iteri (fun i n ->
      if n.Dom.name = "select" && !select_idx = None then select_idx := Some i;
      if n.Dom.name = name then target_idx := Some i
    ) t.open_elements;
    (* Only pop if target exists and is inside select (lower index = closer to current) *)
    (match !target_idx, !select_idx with
     | Some ti, Some si when ti < si ->
       (* Pop until we reach the target *)
       let rec pop_to_target () =
         match t.open_elements with
         | [] -> ()
         | n :: rest ->
           t.open_elements <- rest;
           if n.Dom.name <> name then pop_to_target ()
       in
       pop_to_target ()
     | Some _, Some _ ->
       parse_error t "unexpected-end-tag"
     | Some _, None ->
       (* No select on stack, just pop to target *)
       let rec pop_to_target () =
         match t.open_elements with
         | [] -> ()
         | n :: rest ->
           t.open_elements <- rest;
           if n.Dom.name <> name then pop_to_target ()
       in
       pop_to_target ()
     | None, _ ->
       parse_error t "unexpected-end-tag")
  | Token.EOF ->
    process_in_body t token
  | _ ->
    parse_error t "unexpected-token-in-select"

and process_in_select_in_table t token =
  match token with
  | Token.Tag { kind = Token.Start; name; _ }
    when List.mem name ["caption"; "table"; "tbody"; "tfoot"; "thead"; "tr"; "td"; "th"] ->
    parse_error t "unexpected-start-tag";
    pop_until_tag t "select";
    reset_insertion_mode t;
    process_token t token
  | Token.Tag { kind = Token.End; name; _ }
    when List.mem name ["caption"; "table"; "tbody"; "tfoot"; "thead"; "tr"; "td"; "th"] ->
    parse_error t "unexpected-end-tag";
    if has_element_in_table_scope t name then begin
      pop_until_tag t "select";
      reset_insertion_mode t;
      process_token t token
    end
  | _ ->
    process_in_select t token

and process_in_template t token =
  match token with
  | Token.Character _ | Token.Comment _ | Token.Doctype _ ->
    process_in_body t token
  | Token.Tag { kind = Token.Start; name; _ }
    when List.mem name ["base"; "basefont"; "bgsound"; "link"; "meta"; "noframes"; "script"; "style"; "template"; "title"] ->
    process_in_head t token
  | Token.Tag { kind = Token.End; name = "template"; _ } ->
    process_in_head t token
  | Token.Tag { kind = Token.Start; name; _ }
    when List.mem name ["caption"; "colgroup"; "tbody"; "tfoot"; "thead"] ->
    t.template_modes <- (match t.template_modes with _ :: rest -> rest | [] -> []);
    t.template_modes <- Parser_insertion_mode.In_table :: t.template_modes;
    t.mode <- Parser_insertion_mode.In_table;
    process_token t token
  | Token.Tag { kind = Token.Start; name = "col"; _ } ->
    t.template_modes <- (match t.template_modes with _ :: rest -> rest | [] -> []);
    t.template_modes <- Parser_insertion_mode.In_column_group :: t.template_modes;
    t.mode <- Parser_insertion_mode.In_column_group;
    process_token t token
  | Token.Tag { kind = Token.Start; name = "tr"; _ } ->
    t.template_modes <- (match t.template_modes with _ :: rest -> rest | [] -> []);
    t.template_modes <- Parser_insertion_mode.In_table_body :: t.template_modes;
    t.mode <- Parser_insertion_mode.In_table_body;
    process_token t token
  | Token.Tag { kind = Token.Start; name; _ } when Parser_constants.is_table_cell_element name ->
    t.template_modes <- (match t.template_modes with _ :: rest -> rest | [] -> []);
    t.template_modes <- Parser_insertion_mode.In_row :: t.template_modes;
    t.mode <- Parser_insertion_mode.In_row;
    process_token t token
  | Token.Tag { kind = Token.Start; _ } ->
    t.template_modes <- (match t.template_modes with _ :: rest -> rest | [] -> []);
    t.template_modes <- Parser_insertion_mode.In_body :: t.template_modes;
    t.mode <- Parser_insertion_mode.In_body;
    process_token t token
  | Token.Tag { kind = Token.End; name; _ } ->
    parse_error t ("unexpected-end-tag:" ^ name)
  | Token.EOF ->
    if not (List.exists (fun n -> n.Dom.name = "template" && is_in_html_namespace n) t.open_elements) then
      ()  (* Stop parsing *)
    else begin
      parse_error t "expected-closing-tag-but-got-eof";
      pop_until_html_tag t "template";
      clear_active_formatting_to_marker t;
      t.template_modes <- (match t.template_modes with _ :: rest -> rest | [] -> []);
      reset_insertion_mode t;
      process_token t token
    end

and process_after_body t token =
  match token with
  | Token.Character data when is_whitespace data ->
    process_in_body t token
  | Token.Comment data ->
    (* Insert as last child of html element - html is at bottom of stack *)
    let html_opt = List.find_opt (fun n -> n.Dom.name = "html") t.open_elements in
    (match html_opt with
     | Some html ->
       let location = Dom.make_location ~line:t.current_line ~column:t.current_column () in
       Dom.append_child html (Dom.create_comment ~location data)
     | None -> ())
  | Token.Doctype _ ->
    parse_error t "unexpected-doctype"
  | Token.Tag { kind = Token.Start; name = "html"; _ } ->
    process_in_body t token
  | Token.Tag { kind = Token.End; name = "html"; _ } ->
    if t.fragment_context <> None then
      parse_error t "unexpected-end-tag"
    else
      t.mode <- Parser_insertion_mode.After_after_body
  | Token.EOF ->
    ()  (* Stop parsing *)
  | _ ->
    parse_error t "unexpected-token-after-body";
    t.mode <- Parser_insertion_mode.In_body;
    process_token t token

and process_in_frameset t token =
  match token with
  | Token.Character data ->
    (* Extract only whitespace characters and insert them *)
    let whitespace = String.to_seq data
      |> Seq.filter (fun c -> List.mem c ['\t'; '\n'; '\x0C'; '\r'; ' '])
      |> String.of_seq in
    if whitespace <> "" then insert_character t whitespace;
    if not (is_whitespace data) then
      parse_error t "unexpected-char-in-frameset"
  | Token.Comment data ->
    insert_comment t data
  | Token.Doctype _ ->
    parse_error t "unexpected-doctype"
  | Token.Tag { kind = Token.Start; name = "html"; _ } ->
    process_in_body t token
  | Token.Tag { kind = Token.Start; name = "frameset"; attrs; _ } ->
    ignore (insert_element t "frameset" ~push:true attrs)
  | Token.Tag { kind = Token.End; name = "frameset"; _ } ->
    (match current_node t with
     | Some n when n.Dom.name = "html" -> parse_error t "unexpected-end-tag"
     | _ ->
       pop_current t;
       if t.fragment_context = None then
         (match current_node t with
          | Some n when n.Dom.name <> "frameset" -> t.mode <- Parser_insertion_mode.After_frameset
          | _ -> ()))
  | Token.Tag { kind = Token.Start; name = "frame"; attrs; _ } ->
    ignore (insert_element t "frame" ~push:true attrs);
    pop_current t
  | Token.Tag { kind = Token.Start; name = "noframes"; _ } ->
    process_in_head t token
  | Token.EOF ->
    (match current_node t with
     | Some n when n.Dom.name <> "html" -> parse_error t "expected-closing-tag-but-got-eof"
     | _ -> ())
  | _ ->
    parse_error t "unexpected-token-in-frameset"

and process_after_frameset t token =
  match token with
  | Token.Character data ->
    (* Extract only whitespace characters and insert them *)
    let whitespace = String.to_seq data
      |> Seq.filter (fun c -> List.mem c ['\t'; '\n'; '\x0C'; '\r'; ' '])
      |> String.of_seq in
    if whitespace <> "" then insert_character t whitespace;
    if not (is_whitespace data) then
      parse_error t "unexpected-char-after-frameset"
  | Token.Comment data ->
    insert_comment t data
  | Token.Doctype _ ->
    parse_error t "unexpected-doctype"
  | Token.Tag { kind = Token.Start; name = "html"; _ } ->
    process_in_body t token
  | Token.Tag { kind = Token.End; name = "html"; _ } ->
    t.mode <- Parser_insertion_mode.After_after_frameset
  | Token.Tag { kind = Token.Start; name = "noframes"; _ } ->
    process_in_head t token
  | Token.EOF ->
    ()  (* Stop parsing *)
  | _ ->
    parse_error t "unexpected-token-after-frameset"

and process_after_after_body t token =
  match token with
  | Token.Comment data ->
    insert_comment_to_document t data
  | Token.Doctype _ ->
    process_in_body t token
  | Token.Character data when is_whitespace data ->
    process_in_body t token
  | Token.Tag { kind = Token.Start; name = "html"; _ } ->
    process_in_body t token
  | Token.EOF ->
    ()  (* Stop parsing *)
  | _ ->
    parse_error t "unexpected-token-after-after-body";
    t.mode <- Parser_insertion_mode.In_body;
    process_token t token

and process_after_after_frameset t token =
  match token with
  | Token.Comment data ->
    insert_comment_to_document t data
  | Token.Doctype _ ->
    process_in_body t token
  | Token.Character data ->
    (* Extract only whitespace characters and process using in_body rules *)
    let whitespace = String.to_seq data
      |> Seq.filter (fun c -> List.mem c ['\t'; '\n'; '\x0C'; '\r'; ' '])
      |> String.of_seq in
    if whitespace <> "" then process_in_body t (Token.Character whitespace);
    if not (is_whitespace data) then
      parse_error t "unexpected-char-after-after-frameset"
  | Token.Tag { kind = Token.Start; name = "html"; _ } ->
    process_in_body t token
  | Token.EOF ->
    ()  (* Stop parsing *)
  | Token.Tag { kind = Token.Start; name = "noframes"; _ } ->
    process_in_head t token
  | _ ->
    parse_error t "unexpected-token-after-after-frameset"

and process_token t token =
  (* Check for HTML integration points (SVG foreignObject, desc, title) *)
  let is_html_integration_point node =
    (* SVG foreignObject, desc, and title are always HTML integration points *)
    if node.Dom.namespace = Some "svg" &&
       Parser_constants.is_svg_html_integration node.Dom.name then true
    (* annotation-xml is an HTML integration point only with specific encoding values *)
    else if node.Dom.namespace = Some "mathml" && node.Dom.name = "annotation-xml" then
      match List.assoc_opt "encoding" node.Dom.attrs with
      | Some enc ->
        let enc_lower = String.lowercase_ascii enc in
        enc_lower = "text/html" || enc_lower = "application/xhtml+xml"
      | None -> false
    else false
  in
  (* Check for MathML text integration points *)
  let is_mathml_text_integration_point node =
    node.Dom.namespace = Some "mathml" &&
    Parser_constants.is_mathml_text_integration node.Dom.name
  in
  (* Foreign content handling *)
  let in_foreign =
    match adjusted_current_node t with
    | None -> false
    | Some node ->
      if is_in_html_namespace node then false
      else begin
        (* At HTML integration points, characters and start tags (except mglyph/malignmark) use HTML rules *)
        if is_html_integration_point node then begin
          match token with
          | Token.Character _ -> false
          | Token.Tag { kind = Token.Start; _ } -> false
          | _ -> true
        end
        (* At MathML text integration points, characters and start tags (except mglyph/malignmark) use HTML rules *)
        else if is_mathml_text_integration_point node then begin
          match token with
          | Token.Character _ -> false
          | Token.Tag { kind = Token.Start; name; _ } ->
            name = "mglyph" || name = "malignmark"
          | _ -> true
        end
        (* Special case: <svg> inside annotation-xml uses HTML rules (creates svg in svg namespace) *)
        else if node.Dom.namespace = Some "mathml" && node.Dom.name = "annotation-xml" then begin
          match token with
          | Token.Tag { kind = Token.Start; name; _ } when String.lowercase_ascii name = "svg" -> false
          | _ -> true
        end
        (* Not at integration point - use foreign content rules *)
        (* Breakout handling is done inside process_foreign_content *)
        else true
      end
  in

  (* Check if at HTML integration point for special table mode handling *)
  let at_integration_point =
    match adjusted_current_node t with
    | Some node ->
      is_html_integration_point node || is_mathml_text_integration_point node
    | None -> false
  in

  if in_foreign then
    process_foreign_content t token
  else if at_integration_point then begin
    (* At integration points, check if in table mode without table in scope *)
    let is_table_mode = List.mem t.mode [In_table; In_table_body; In_row; In_cell; In_caption; In_column_group] in
    let has_table = has_element_in_table_scope t "table" in
    if is_table_mode && not has_table then begin
      match token with
      | Token.Tag { kind = Token.Start; _ } ->
        (* Temporarily use IN_BODY for start tags in table mode without table *)
        let saved_mode = t.mode in
        t.mode <- In_body;
        process_by_mode t token;
        if t.mode = In_body then t.mode <- saved_mode
      | _ -> process_by_mode t token
    end else
      process_by_mode t token
  end else
    process_by_mode t token

(* Pop foreign elements until HTML or integration point *)
and pop_until_html_or_integration_point t =
  let is_html_integration_point node =
    (* SVG foreignObject, desc, and title are always HTML integration points *)
    if node.Dom.namespace = Some "svg" &&
       Parser_constants.is_svg_html_integration node.Dom.name then true
    (* annotation-xml is an HTML integration point only with specific encoding values *)
    else if node.Dom.namespace = Some "mathml" && node.Dom.name = "annotation-xml" then
      match List.assoc_opt "encoding" node.Dom.attrs with
      | Some enc ->
        let enc_lower = String.lowercase_ascii enc in
        enc_lower = "text/html" || enc_lower = "application/xhtml+xml"
      | None -> false
    else false
  in
  (* Get fragment context element - only for foreign namespace fragment contexts *)
  let fragment_context_elem = t.fragment_context_element in
  let rec pop () =
    match current_node t with
    | None -> ()
    | Some node ->
      if is_in_html_namespace node then ()
      else if is_html_integration_point node then ()
      (* Don't pop past fragment context element *)
      else (match fragment_context_elem with
        | Some ctx when node == ctx -> ()
        | _ ->
          pop_current t;
          pop ())
  in
  pop ()

(* Foreign breakout elements - these break out of foreign content *)
and is_foreign_breakout_element name =
  List.mem (String.lowercase_ascii name)
    ["b"; "big"; "blockquote"; "body"; "br"; "center"; "code"; "dd"; "div"; "dl"; "dt";
     "em"; "embed"; "h1"; "h2"; "h3"; "h4"; "h5"; "h6"; "head"; "hr"; "i"; "img"; "li";
     "listing"; "menu"; "meta"; "nobr"; "ol"; "p"; "pre"; "ruby"; "s"; "small"; "span";
     "strong"; "strike"; "sub"; "sup"; "table"; "tt"; "u"; "ul"; "var"]

and process_foreign_content t token =
  match token with
  | Token.Character data when String.contains data '\x00' ->
    (* Replace NUL characters with U+FFFD replacement character *)
    parse_error t "unexpected-null-character";
    let buf = Buffer.create (String.length data) in
    let has_non_ws_non_nul = ref false in
    String.iter (fun c ->
      if c = '\x00' then Buffer.add_string buf "\xEF\xBF\xBD"
      else begin
        Buffer.add_char buf c;
        if not (c = ' ' || c = '\t' || c = '\n' || c = '\x0C' || c = '\r') then
          has_non_ws_non_nul := true
      end
    ) data;
    let replaced = Buffer.contents buf in
    insert_character t replaced;
    (* Only set frameset_ok to false if there's actual non-whitespace non-NUL content *)
    if !has_non_ws_non_nul then t.frameset_ok <- false
  | Token.Character data when is_whitespace data ->
    insert_character t data
  | Token.Character data ->
    insert_character t data;
    t.frameset_ok <- false
  | Token.Comment data ->
    insert_comment t data
  | Token.Doctype _ ->
    parse_error t "unexpected-doctype"
  | Token.Tag { kind = Token.Start; name; _ } when is_foreign_breakout_element name ->
    (* Breakout from foreign content - pop until HTML or integration point, reprocess in HTML mode *)
    parse_error t "unexpected-html-element-in-foreign-content";
    pop_until_html_or_integration_point t;
    reset_insertion_mode t;
    (* Use process_by_mode to force HTML mode processing and avoid infinite loop *)
    process_by_mode t token
  | Token.Tag { kind = Token.Start; name = "font"; attrs; _ }
    when List.exists (fun (n, _) ->
      let n = String.lowercase_ascii n in
      n = "color" || n = "face" || n = "size") attrs ->
    (* font with color/face/size breaks out of foreign content *)
    parse_error t "unexpected-html-element-in-foreign-content";
    pop_until_html_or_integration_point t;
    reset_insertion_mode t;
    process_by_mode t token
  | Token.Tag { kind = Token.Start; name; attrs; self_closing } ->
    let name =
      match adjusted_current_node t with
      | Some n when n.Dom.namespace = Some "svg" -> Parser_constants.adjust_svg_tag_name name
      | _ -> name
    in
    let attrs =
      match adjusted_current_node t with
      | Some n when n.Dom.namespace = Some "svg" ->
        Parser_constants.adjust_svg_attrs (Parser_constants.adjust_foreign_attrs attrs)
      | Some n when n.Dom.namespace = Some "mathml" ->
        Parser_constants.adjust_mathml_attrs (Parser_constants.adjust_foreign_attrs attrs)
      | _ -> Parser_constants.adjust_foreign_attrs attrs
    in
    let namespace =
      match adjusted_current_node t with
      | Some n -> n.Dom.namespace
      | None -> None
    in
    let node = insert_element t name ~namespace attrs in
    t.open_elements <- node :: t.open_elements;
    if self_closing then pop_current t
  | Token.Tag { kind = Token.End; name; _ } when List.mem (String.lowercase_ascii name) ["br"; "p"] ->
    (* Special case: </br> and </p> end tags trigger breakout from foreign content *)
    parse_error t "unexpected-html-element-in-foreign-content";
    pop_until_html_or_integration_point t;
    reset_insertion_mode t;
    (* Use process_by_mode to force HTML mode processing and avoid infinite loop *)
    process_by_mode t token
  | Token.Tag { kind = Token.End; name; _ } ->
    (* Find matching element per WHATWG spec for foreign content *)
    let is_fragment_context n =
      match t.fragment_context_element with
      | Some ctx -> n == ctx
      | None -> false
    in
    let name_lower = String.lowercase_ascii name in
    (* Walk through stack looking for matching element *)
    let rec find_and_process first_node idx = function
      | [] -> () (* Stack exhausted - ignore tag *)
      | n :: rest ->
        let node_name_lower = String.lowercase_ascii n.Dom.name in
        let is_html = is_in_html_namespace n in
        let name_matches = node_name_lower = name_lower in

        (* If first node doesn't match tag name, it's a parse error *)
        if first_node && not name_matches then
          parse_error t "unexpected-end-tag-in-foreign-content";

        (* Check if this node matches the end tag *)
        if name_matches then begin
          (* Fragment context check *)
          if is_fragment_context n then
            parse_error t "unexpected-end-tag-in-fragment-context"
          (* If matched element is in HTML namespace, reprocess via HTML mode *)
          else if is_html then
            process_by_mode t token
          (* Otherwise it's a foreign element - pop everything from this point up *)
          else begin
            (* Pop all elements from current down to and including the matched element *)
            let rec pop_to_idx current_idx =
              if current_idx >= idx then begin
                pop_current t;
                pop_to_idx (current_idx - 1)
              end
            in
            pop_to_idx (List.length t.open_elements - 1)
          end
        end
        (* If we hit an HTML element that doesn't match, process via HTML mode *)
        else if is_html then
          process_by_mode t token
        (* Continue searching in the stack *)
        else
          find_and_process false (idx - 1) rest
    in
    find_and_process true (List.length t.open_elements - 1) t.open_elements
  | Token.EOF ->
    process_by_mode t token

and process_by_mode t token =
  match t.mode with
  | Parser_insertion_mode.Initial -> process_initial t token
  | Parser_insertion_mode.Before_html -> process_before_html t token
  | Parser_insertion_mode.Before_head -> process_before_head t token
  | Parser_insertion_mode.In_head -> process_in_head t token
  | Parser_insertion_mode.In_head_noscript -> process_in_head_noscript t token
  | Parser_insertion_mode.After_head -> process_after_head t token
  | Parser_insertion_mode.In_body -> process_in_body t token
  | Parser_insertion_mode.Text -> process_text t token
  | Parser_insertion_mode.In_table -> process_in_table t token
  | Parser_insertion_mode.In_table_text -> process_in_table_text t token
  | Parser_insertion_mode.In_caption -> process_in_caption t token
  | Parser_insertion_mode.In_column_group -> process_in_column_group t token
  | Parser_insertion_mode.In_table_body -> process_in_table_body t token
  | Parser_insertion_mode.In_row -> process_in_row t token
  | Parser_insertion_mode.In_cell -> process_in_cell t token
  | Parser_insertion_mode.In_select -> process_in_select t token
  | Parser_insertion_mode.In_select_in_table -> process_in_select_in_table t token
  | Parser_insertion_mode.In_template -> process_in_template t token
  | Parser_insertion_mode.After_body -> process_after_body t token
  | Parser_insertion_mode.In_frameset -> process_in_frameset t token
  | Parser_insertion_mode.After_frameset -> process_after_frameset t token
  | Parser_insertion_mode.After_after_body -> process_after_after_body t token
  | Parser_insertion_mode.After_after_frameset -> process_after_after_frameset t token

(* Populate selectedcontent elements with content from selected option *)
let find_elements name node =
  let result = ref [] in
  let rec find n =
    if n.Dom.name = name then result := n :: !result;
    List.iter find n.Dom.children
  in
  find node;
  List.rev !result  (* Reverse to maintain document order *)

let find_element name node =
  let rec find n =
    if n.Dom.name = name then Some n
    else
      List.find_map find n.Dom.children
  in
  find node

let populate_selectedcontent document =
  let selects = find_elements "select" document in
  List.iter (fun select ->
    match find_element "selectedcontent" select with
    | None -> ()
    | Some selectedcontent ->
      let options = find_elements "option" select in
      if options <> [] then begin
        (* Find selected option or use first *)
        let selected_option =
          match List.find_opt (fun opt -> Dom.has_attr opt "selected") options with
          | Some opt -> opt
          | None -> List.hd options
        in
        (* Clone children from selected option to selectedcontent *)
        List.iter (fun child ->
          let cloned = Dom.clone ~deep:true child in
          Dom.append_child selectedcontent cloned
        ) selected_option.Dom.children
      end
  ) selects

let finish t =
  (* Populate selectedcontent elements *)
  populate_selectedcontent t.document;
  (* For fragment parsing, remove the html wrapper and promote children *)
  if t.fragment_context <> None then begin
    match t.document.Dom.children with
    | [root] when root.Dom.name = "html" ->
      (* Move context element's children to root if applicable *)
      (match t.fragment_context_element with
      | Some ctx_elem ->
        (match ctx_elem.Dom.parent with
        | Some p when p == root ->
          let ctx_children = ctx_elem.Dom.children in
          List.iter (fun child ->
            Dom.remove_child ctx_elem child;
            Dom.append_child root child
          ) ctx_children;
          Dom.remove_child root ctx_elem
        | _ -> ())
      | None -> ());
      (* Promote root's children to document - preserve order *)
      let children_copy = root.Dom.children in
      List.iter (fun child ->
        Dom.remove_child root child;
        Dom.append_child t.document child
      ) children_copy;
      Dom.remove_child t.document root
    | _ -> ()
  end;
  t.document

let get_errors t = List.rev t.errors