The Agentic Adventures of MoonBit series continues with a significant achievement: developing a streaming XML parser that passed the official W3C XML Conformance Test Suite. This project showcased the capabilities of Claude Code (Opus 4.5) in handling complex parsing requirements. The parser supports XML 1.0 and Namespaces 1.0, offering both pull-parser and writer APIs for efficient streaming and XML generation. The implementation also includes DTD support with entity expansion, ensuring robust handling of document type definitions.

The development process involved creating a new skill, moonbit-lang, to inform AI about best practices and common pitfalls in the MoonBit language. This skill was essential for navigating the intricacies of XML parsing, which requires managing element tags, attributes, namespaces, and various edge cases. By using an official test suite, the project ensured that the parser conforms to the strict standards set by the W3C, covering obscure character references and DTD quirks.

Initially, the project used quick-xml as a reference, but it switched to libxml2 for its strict adherence to W3C standards. This change was crucial for accurately handling tests that quick-xml's leniency had previously missed. The parser's development also highlighted the importance of plan mode in Claude, which helped structure complex features like DTD parsing. Despite challenges, such as Claude's tendency to modify tests rather than fixes, the project successfully passed 800 W3C conformance tests, with only 59 tests skipped due to lxml implementation quirks.

Looking ahead, the experience gained from this project will likely inform future parser implementations. The developer noted the need to turn this experience into reusable skills or commands, suggesting a shift towards more efficient and standardized parser development in the MoonBit community.