Break the 2,320-line monolithic lib.rs into focused modules: - node.rs: Attribute, ElementData, NodeKind, Node types - document.rs: Document struct/impl and TreeIterator - tests/: 6 topic-based test files (basic, node_type, tree_ops, sibling, inner_html, dirty_flag) Public API unchanged; all 92 tests pass in their new locations. Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>