Bindings between boa-cat (JS engine) and the DOM (html-cat tree) plus fetch (net-cat). v0.7.12 extends the v0.7.8 selector grammar with sibling combinators: `a + b` (adjacent sibling -- b's immediately-preceding sibling matches a) and `a ~ b` (general sibling -- any of b's preceding siblings matches a). Both walk the parent's children array via the existing `__parent__` backref to compute sibling relationships. Combines with all existing combinators (`section h2 + p`, etc.) and reaches scripts through both `querySelector` and `querySelectorAll`. Seventh sub-crate of a Servo-replacement webview runtime targeting Tauri.