Constant SELECT_ELEMENT_JS 

pub const SELECT_ELEMENT_JS: &str = r#"
(function() {
    function cssPath(el) {
        if (!(el instanceof Element)) return '';
        const path = [];
        while (el && el.nodeType === 1) {
            let selector = el.nodeName.toLowerCase();
            if (el.id) { selector += '#' + el.id; path.unshift(selector); break; }
            else {
                let sib = el, nth = 1;
                while ((sib = sib.previousElementSibling)) { if (sib.nodeName === el.nodeName) nth++; }
                selector += ':nth-of-type(' + nth + ')';
            }
            path.unshift(selector);
            el = el.parentNode;
        }
        return path.join(' > ');
    }
    return new Promise((resolve) => {
        const overlay = document.createElement('div');
        overlay.style.cssText = 'position:fixed;inset:0;z-index:2147483647;cursor:crosshair;background:rgba(0,150,255,0.05);';
        document.body.appendChild(overlay);
        overlay.addEventListener('click', (e) => {
            e.preventDefault(); e.stopPropagation();
            overlay.remove();
            const x = e.clientX, y = e.clientY;
            const el = document.elementFromPoint(x, y);
            resolve(cssPath(el));
        }, { capture: true, once: true });
    });
})()
"#;

Interactive element picker. Resolves with the selector string for the picked element.