Worked on enhancing XML DOCTYPE parsing across the JunkFood02/ladybird and SerenityOS/serenity repositories, focusing on improving standards compliance and downstream tooling reliability. Addressed issues in LibXML by introducing a set_doctype method within XMLDocumentBuilder and updating the Parser to capture and store public and system identifiers after parsing. Added targeted tests to validate DOCTYPE parsing, aligning results with Web Platform Test expectations. Utilized C++ and HTML, applying skills in DOM manipulation and XML parsing to ensure accurate document structure representation. The work resulted in more consistent and reliable DOM parsing behavior across both projects, supporting better interoperability and testing outcomes.