note 16250 rejected from ref.url by zak

A function to parse relative URLs is conspicuously missing. What would be nice is a function like parse_relative_url(url, url_base). url would be the URL string, as in parse_url(). url_base would be an optional parameter that contains the context URL. The default for url_base would be the URL of the currently executing script. This function could be useful for scripts that allow a "callback" to another script. When Script A invokes Script B, it includes a parameter of a callback script (the relative URL of Script A or even Script C) that Script B calls after it finishes.