When a fragment updates cannot find the requested element, Unpoly will try this list of alternative selectors.
The first selector that matches an element in the current page (or response) will be used.
If the response contains none of the selectors, an error message will be shown.
It is recommend to always keep 'body' as the last selector in the last in the case
your server or load balancer renders an error message that does not contain your
application layout.
