Worked on the w3ctag/design-principles repository to introduce a new API design guideline focused on improving the safety and clarity of web APIs. Developed and documented the principle that side-effectful functions should return undefined, aligning with Command-Query Separation to support safer future evolution and clearer semantics for API consumers. The implementation included an illustrative example using HTML and JavaScript, specifically referencing HTMLMediaElement.play(), to demonstrate the benefits of this approach. Emphasized API design best practices and web standards, while collaborating across teams and ensuring version control traceability. No bug fixes were recorded during this period, with work centered on feature development.