> You may have also noticed that cookies follow a similar, but different format: x=1;y=2 which doesn’t actually conflict with HTML character encoding at all. This idea was not lost on the W3C, who encouraged implementers to support ; as well as & in query parameters as early as 1995.
I wish the w3c had won that one.
I think & is a valid character for path names. You probably need the ? to know the query has begun.