Bindings between boa-cat (JS engine) and the DOM (html-cat tree) plus fetch (net-cat). v0.6.1 opens DOM mutation: `document.createElement(tag)` allocates a fresh element-shaped Object with the requested tagName and empty fields; `Element.appendChild(child)` mutates the children array in-place and returns the appended child. Both compose with the existing `extract_document` back-prop so newly-created and newly-appended nodes reach layout / paint on the next eval pass. Seventh sub-crate of a Servo-replacement webview runtime targeting Tauri.