Really, we should say `/[&?from]`... so we don't trip over params called "came_from" or whatever in the future. After landing this, maybe we can go back and factor up all those times we ad-hoc grepped the query string. I could see us easily getting into a URL-decoding bug if we ever used a decoded query string for something other than reconstituting a URL. There are some good ideas at https://stackoverflow.com/questions/901115/how-can-i-get-query-string-values-in-javascript.