I'm wondering if it's possible to determine WP_Query parameters by only using the given page URL. The reason I'm trying to do this because I'm developing a SPA theme (and ultimately a JSON response) ...
OK, so I've created a page (http://justinhealth.com/testsite/error-signing-up). It's a custom error page for iContact. Now, when there's an error in iContact's signup, it actually goes here: ...