Constant GET_DOM_JS 

pub const GET_DOM_JS: &str = r#"
(function(selector) {
    const root = selector ? document.querySelector(selector) : document.documentElement;
    if (!root) return null;
    if (typeof root.getHTML === 'function') {
        try { return root.getHTML({ serializableShadowRoots: true }); } catch (e) {}
    }
    return root.outerHTML;
})
"#;

Serializes the DOM with shadow roots included.