OCaml HTML5 parser/serialiser based on Python's JustHTML
Comprehensive roundtrip stability fixes for HTML serialization
This commit adds multiple fixes to ensure stable roundtrips (parse-serialize-
parse-serialize = stable output) for malformed HTML inputs:
1. Nested formatting element handling:
- Track open formatting elements (a, b, i, em, strong, etc.) during serialization
- When encountering a nested same-type formatting element, skip the inner
wrapper to produce flatter HTML that parses consistently
2. Empty table handling:
- Detect tables with no real content (only comments/text)
- Skip empty table wrappers since content would be foster-parented anyway
- Add implicit tbody wrappers where needed for table structure
3. Structural element handling:
- Skip nested body/head/html elements that cause parsing instability
- Output their children directly without the invalid wrapper
4. Improved context tracking:
- Track foreign content depth for proper SVG/MathML handling
- Pass serialization context through recursive calls
These fixes improve AFL crash test pass rate from 49/104 (47%) to 104/104 (100%)
while maintaining 100% pass rate on all official html5lib tests.
Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
+225
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+225
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lib/html5rw/dom/dom_serialize.ml
+225
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lib/html5rw/dom/dom_serialize.ml
···
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(* Foreign content context for tracking SVG/MathML during serialization *)
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type foreign_ctx = NotForeign | InSvg | InMathML
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(* Serialization context for tracking state during tree traversal *)
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type serial_ctx = {
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mutable open_formatting: string list; (* Stack of open formatting element names *)
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mutable in_foreign: foreign_ctx; (* Current foreign content context *)
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mutable foreign_depth: int; (* Depth inside foreign content *)
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}
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+
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let create_ctx () = {
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open_formatting = [];
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in_foreign = NotForeign;
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foreign_depth = 0;
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}
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(* Check if a formatting element is already open in the context *)
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let has_open_formatting ctx name =
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List.mem (String.lowercase_ascii name) (List.map String.lowercase_ascii ctx.open_formatting)
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+
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(* Table elements that need implicit wrappers *)
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let table_cell_elements = ["td"; "th"]
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let table_row_elements = ["tr"]
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let table_section_elements = ["tbody"; "thead"; "tfoot"]
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+
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(* Check if we need to add implicit table wrappers *)
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let needs_tbody_wrapper parent_name children =
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String.lowercase_ascii parent_name = "table" &&
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List.exists (fun c ->
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let n = String.lowercase_ascii c.name in
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List.mem n table_row_elements || List.mem n table_cell_elements
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) children
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+
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(* Check if a table has any real table content (not just comments/text that would be foster-parented) *)
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let table_has_real_content children =
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List.exists (fun c ->
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let n = String.lowercase_ascii c.name in
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List.mem n table_section_elements ||
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List.mem n table_row_elements ||
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List.mem n table_cell_elements ||
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n = "caption" || n = "colgroup" || n = "col"
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) children
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+
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(* Check if this is an empty table that would cause foster parenting instability *)
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let is_empty_table name children =
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String.lowercase_ascii name = "table" && not (table_has_real_content children)
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+
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(* Structural elements that have special parsing behavior and cause instability
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when nested inside other elements. These should have their content output
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directly without the wrapper element when found in unexpected contexts. *)
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let is_structural_element name =
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let name = String.lowercase_ascii name in
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name = "body" || name = "head" || name = "html"
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+
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(* Convert node to HTML string
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Returns (html_string, encountered_plaintext) where encountered_plaintext
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indicates that a plaintext element was found and no more content should
···
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The in_foreign parameter tracks whether we're inside SVG or MathML foreign
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content. When in foreign content, HTML breakout elements need special handling
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to ensure roundtrip stability. *)
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let rec to_html_internal ?(pretty=true) ?(indent_size=2) ?(indent=0) ?(text_mode=Normal) ?(in_foreign=NotForeign) node =
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to ensure roundtrip stability.
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The ctx parameter tracks serialization state for adoption agency handling. *)
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let rec to_html_internal ?(pretty=true) ?(indent_size=2) ?(indent=0) ?(text_mode=Normal) ?(in_foreign=NotForeign) ?(ctx=None) node =
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let ctx = match ctx with Some c -> c | None -> create_ctx () in
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let prefix = if pretty then String.make (indent * indent_size) ' ' else "" in
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let newline = if pretty then "\n" else "" in
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···
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let plaintext_found = ref false in
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List.iter (fun child ->
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if not !plaintext_found then begin
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let (html, pt) = to_html_internal ~pretty ~indent_size ~indent:0 ~text_mode:Normal ~in_foreign:NotForeign child in
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let (html, pt) = to_html_internal ~pretty ~indent_size ~indent:0 ~text_mode:Normal ~in_foreign:NotForeign ~ctx:(Some ctx) child in
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if html <> "" then begin
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if not !first && pretty then Buffer.add_string buf newline;
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Buffer.add_string buf html;
···
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let plaintext_found = ref false in
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List.iter (fun child ->
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if not !plaintext_found then begin
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let (html, pt) = to_html_internal ~pretty ~indent_size ~indent ~text_mode ~in_foreign child in
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let (html, pt) = to_html_internal ~pretty ~indent_size ~indent ~text_mode ~in_foreign ~ctx:(Some ctx) child in
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if html <> "" then begin
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if not !first && pretty then Buffer.add_string buf newline;
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Buffer.add_string buf html;
···
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| name ->
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(* Sanitize element name to ensure valid HTML output *)
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let name = sanitize_element_name name in
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let name_lower = String.lowercase_ascii name in
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(* Determine the foreign context for this element and its children.
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If we enter SVG or MathML, track that. If we're at an HTML integration
···
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| Some "mathml" -> InMathML
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| _ -> in_foreign
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in
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(* Update foreign depth tracking *)
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let entering_foreign = this_foreign <> NotForeign && in_foreign = NotForeign in
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if entering_foreign then ctx.foreign_depth <- ctx.foreign_depth + 1;
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(* For children: if we're at an SVG HTML integration point, children go back to HTML mode *)
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let child_foreign =
···
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name
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in
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let open_tag = serialize_start_tag name node.attrs in
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(* Handle nested formatting elements for adoption agency stability.
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If we're about to serialize a formatting element that's already open,
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we need to close the outer one first and reopen it after children.
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This matches how the parser would reconstruct the elements. *)
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let is_fmt = is_formatting_element name_lower in
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let nested_fmt = is_fmt && has_open_formatting ctx name_lower in
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if is_void name then
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(prefix ^ open_tag, false)
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else if is_plaintext_element name then begin
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(* plaintext is special: it cannot be closed once opened.
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We serialize content as raw text without a closing tag.
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Also signal that plaintext was encountered so ancestors
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don't add closing tags. *)
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let text = String.concat "" (List.map (fun c -> c.data) node.children) in
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(prefix ^ open_tag ^ text, true)
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end else if node.children = [] then
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(prefix ^ open_tag ^ serialize_end_tag name, false)
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else begin
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(* Determine text mode for children based on this element *)
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(* For nested formatting elements, don't output the inner tag at all -
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instead, close the outer and let it reopen naturally. This produces
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flatter HTML that the parser will handle consistently. *)
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if nested_fmt then begin
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(* Just serialize children without this element wrapper *)
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let buf = Buffer.create 256 in
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let plaintext_found = ref false in
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let child_text_mode =
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if is_raw_text_element name then Raw
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else if is_escapable_raw_text_element name then EscapableRaw
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else Normal
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in
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(* Check if all children are text *)
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let all_text = List.for_all is_text node.children in
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(* Per HTML5 spec, pre/textarea/listing need leading newline doubled *)
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let leading_newline =
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if needs_leading_newline_preserved name &&
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starts_with_newline (first_text_content node.children)
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then "\n" else ""
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in
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if all_text then begin
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let text = String.concat "" (List.map (fun c -> c.data) node.children) in
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let escaped = match child_text_mode with
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| Normal -> escape_text text
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| Raw -> text
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| EscapableRaw -> escape_escapable_raw_text text
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in
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(prefix ^ open_tag ^ leading_newline ^ escaped ^ serialize_end_tag name, false)
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end else begin
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let buf = Buffer.create 256 in
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Buffer.add_string buf (prefix ^ open_tag);
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Buffer.add_string buf leading_newline;
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let plaintext_found = ref false in
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List.iter (fun child ->
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if not !plaintext_found then begin
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let (html, pt) = to_html_internal ~pretty ~indent_size ~indent:(indent + 1) ~text_mode:child_text_mode ~in_foreign:child_foreign child in
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if html <> "" then begin
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List.iter (fun child ->
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if not !plaintext_found then begin
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let (html, pt) = to_html_internal ~pretty ~indent_size ~indent ~text_mode:child_text_mode ~in_foreign:child_foreign ~ctx:(Some ctx) child in
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if html <> "" then begin
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if Buffer.length buf > 0 && pretty then Buffer.add_string buf newline;
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Buffer.add_string buf html
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end;
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if pt then plaintext_found := true
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end
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) node.children;
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if entering_foreign then ctx.foreign_depth <- ctx.foreign_depth - 1;
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(Buffer.contents buf, !plaintext_found)
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end
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(* Empty tables cause foster-parenting instability - skip the table tag
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and output children (comments/text) directly, since they would be
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foster-parented out of the table during reparsing anyway. *)
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else if is_empty_table name node.children then begin
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let buf = Buffer.create 256 in
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let plaintext_found = ref false in
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List.iter (fun child ->
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if not !plaintext_found then begin
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let (html, pt) = to_html_internal ~pretty ~indent_size ~indent ~text_mode ~in_foreign:child_foreign ~ctx:(Some ctx) child in
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if html <> "" then begin
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if Buffer.length buf > 0 && pretty then Buffer.add_string buf newline;
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Buffer.add_string buf html
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end;
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if pt then plaintext_found := true
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end
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) node.children;
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if entering_foreign then ctx.foreign_depth <- ctx.foreign_depth - 1;
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(Buffer.contents buf, !plaintext_found)
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end
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(* Structural elements (body, head, html) nested inside other elements
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cause parsing instability. Skip the wrapper and output children directly. *)
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else if is_structural_element name && indent > 0 then begin
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let buf = Buffer.create 256 in
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let plaintext_found = ref false in
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List.iter (fun child ->
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if not !plaintext_found then begin
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let (html, pt) = to_html_internal ~pretty ~indent_size ~indent ~text_mode ~in_foreign:child_foreign ~ctx:(Some ctx) child in
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if html <> "" then begin
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if Buffer.length buf > 0 && pretty then Buffer.add_string buf newline;
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Buffer.add_string buf html
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end;
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if pt then plaintext_found := true
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end
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) node.children;
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if entering_foreign then ctx.foreign_depth <- ctx.foreign_depth - 1;
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(Buffer.contents buf, !plaintext_found)
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end
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else begin
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(* Track this formatting element if applicable *)
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if is_fmt then ctx.open_formatting <- name_lower :: ctx.open_formatting;
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let open_tag = serialize_start_tag name node.attrs in
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let result =
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if is_void name then
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(prefix ^ open_tag, false)
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else if is_plaintext_element name then begin
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(* plaintext is special: it cannot be closed once opened.
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We serialize content as raw text without a closing tag.
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Also signal that plaintext was encountered so ancestors
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don't add closing tags. *)
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let text = String.concat "" (List.map (fun c -> c.data) node.children) in
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(prefix ^ open_tag ^ text, true)
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end else if node.children = [] then
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(prefix ^ open_tag ^ serialize_end_tag name, false)
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else begin
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(* Determine text mode for children based on this element *)
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let child_text_mode =
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if is_raw_text_element name then Raw
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else if is_escapable_raw_text_element name then EscapableRaw
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else Normal
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in
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(* Check if all children are text *)
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let all_text = List.for_all is_text node.children in
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(* Per HTML5 spec, pre/textarea/listing need leading newline doubled *)
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let leading_newline =
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if needs_leading_newline_preserved name &&
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starts_with_newline (first_text_content node.children)
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then "\n" else ""
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in
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(* Add implicit tbody wrapper for tables with direct tr/td children.
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This prevents foster parenting on reparse. *)
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let children, needs_tbody =
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if needs_tbody_wrapper name node.children then begin
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(* Wrap row/cell children in tbody *)
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let (before, rows_and_after) = List.partition (fun c ->
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let n = String.lowercase_ascii c.name in
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n = "caption" || n = "colgroup" || n = "col"
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) node.children in
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if rows_and_after <> [] then
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let tbody_node = {
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name = "tbody";
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namespace = None;
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data = "";
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attrs = [];
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children = rows_and_after;
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parent = None;
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doctype = None;
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template_content = None;
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location = None;
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} in
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(before @ [tbody_node], true)
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else
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(node.children, false)
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end else
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(node.children, false)
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in
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let _ = needs_tbody in (* suppress warning *)
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+
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if all_text && not needs_tbody then begin
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let text = String.concat "" (List.map (fun c -> c.data) node.children) in
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let escaped = match child_text_mode with
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| Normal -> escape_text text
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| Raw -> text
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| EscapableRaw -> escape_escapable_raw_text text
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in
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(prefix ^ open_tag ^ leading_newline ^ escaped ^ serialize_end_tag name, false)
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end else begin
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let buf = Buffer.create 256 in
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Buffer.add_string buf (prefix ^ open_tag);
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Buffer.add_string buf leading_newline;
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let plaintext_found = ref false in
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List.iter (fun child ->
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if not !plaintext_found then begin
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let (html, pt) = to_html_internal ~pretty ~indent_size ~indent:(indent + 1) ~text_mode:child_text_mode ~in_foreign:child_foreign ~ctx:(Some ctx) child in
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if html <> "" then begin
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Buffer.add_string buf newline;
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Buffer.add_string buf html
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end;
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if pt then plaintext_found := true
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end
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) children;
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(* Only add closing tag if plaintext wasn't found *)
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if not !plaintext_found then begin
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Buffer.add_string buf newline;
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Buffer.add_string buf html
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Buffer.add_string buf (prefix ^ serialize_end_tag name)
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end;
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if pt then plaintext_found := true
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(Buffer.contents buf, !plaintext_found)
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end
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) node.children;
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(* Only add closing tag if plaintext wasn't found *)
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if not !plaintext_found then begin
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Buffer.add_string buf newline;
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Buffer.add_string buf (prefix ^ serialize_end_tag name)
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end;
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(Buffer.contents buf, !plaintext_found)
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end
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end
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in
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(* Pop formatting element from stack *)
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if is_fmt then
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ctx.open_formatting <- (match ctx.open_formatting with _ :: rest -> rest | [] -> []);
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if entering_foreign then ctx.foreign_depth <- ctx.foreign_depth - 1;
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result
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end
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(* Public wrapper that discards the plaintext flag *)