feat(ie-html): implement core HTML tree builder state machine #57

WHATWG tree construction with basic insertion modes:
- TreeBuilder struct: open elements stack, head/form pointers,
  insertion mode tracking, pending text accumulation
- ParseResult: document + errors + style_elements + link_stylesheets
- Insertion modes: Initial, BeforeHtml, BeforeHead, InHead,
  InHeadNoscript, AfterHead, InBody, Text, AfterBody, AfterAfterBody
- InBody handles: block elements (div, p, ul, etc.), headings (h1-h6
  with nesting fix), void elements (br, hr, img, input), inline
  elements (basic push/pop), form handling
- Core operations: insert_element with attributes, insert_character
  with text node coalescing, insert_comment, generate_implied_end_tags,
  scope checking (regular + button scope), close_p_element
- Tokenizer integration: state switching for script (ScriptData),
  style/noframes (RawText), title/textarea (RcData)
- Text mode: captures style content → style_elements, link hrefs →
  link_stylesheets
- Implicit element creation: html, head, body auto-inserted
- 12 unit tests covering document structure, implicit elements,
  void elements, style/link extraction, nesting, comments, doctype

Author: thomasnemer

crates/ie-html/src/insertion_mode.rs

@@ -0,0 +1,26 @@
+#[derive(Debug, Clone, Copy, PartialEq)]
+pub enum InsertionMode {
+    Initial,
+    BeforeHtml,
+    BeforeHead,
+    InHead,
+    InHeadNoscript,
+    AfterHead,
+    InBody,
+    Text,
+    InTable,
+    InTableText,
+    InCaption,
+    InColumnGroup,
+    InTableBody,
+    InRow,
+    InCell,
+    InSelect,
+    InSelectInTable,
+    InTemplate,
+    AfterBody,
+    InFrameset,
+    AfterFrameset,
+    AfterAfterBody,
+    AfterAfterFrameset,
+}

crates/ie-html/src/lib.rs

@@ -4,10 +4,11 @@
 //! Targets latest spec only — no quirks mode, no legacy element support.
 
 pub mod entities;
+pub mod insertion_mode;
 pub mod token;
 pub mod tokenizer;
 pub mod tree_builder;
 
 pub use token::Token;
 pub use tokenizer::Tokenizer;
-pub use tree_builder::parse;
+pub use tree_builder::{ParseResult, parse};