HTML streaming allows servers to send HTML progressively rather than in one chunk, enabling browsers to render content as it arrives. HTMS is an experimental project that extends basic streaming with progressive placeholders that can be updated asynchronously within a single HTTP response. This approach delivers early First Contentful Paint, maintains SEO-friendly complete HTML documents, and achieves strong Lighthouse scores without client-side hydration. The technique works best combined with SSR, SSG, or tools like HTMX, though it introduces constraints around error handling once streaming begins and requires careful layout planning.