Older browsers do not support CSS selector in queries, this means you'll need external polyfills for this.
The suggested polyfill is Sizzle, require it before opal-browser.
Older browsers don't support JSON parsing natively, this means you'll need external polyfills for this.
The suggested polyfill is json2, require it before opal-browser.
Not all browsers support XPath queries, I'm looking at you Internet Explorer, this means you'll need external polyfills for this.
The suggested polyfill is wgxpath, require it before opal-browser.