Worked on the apostrophecms/apostrophe repository to address a specific HTML sanitization issue affecting front-end rendering. Focused on stabilizing HTML output by ensuring that the <col> element is treated as a self-closing tag during sanitization, which prevents invalid HTML from appearing in editors and user-facing templates. Updated the sanitize-html configuration and introduced regression tests to verify the correct handling of <col> tags, thereby reducing layout inconsistencies and support requests. Utilized JavaScript for both the implementation and testing phases, applying front end development and HTML sanitization skills to improve the reliability of content rendering across the platform.