вт, 7 июн. 2022 г., 03:10 Gavin Lambert via Boost
file is also an URL protocol, although you're correct that mailto is not. I don't think anyone actually types mailto: addresses into the address bar on a browser, though (nor can I think of any other URIs that someone might manually type, except for things like about:config that are browser-specific).
There's no such thing as "URL protocol". The distinction between a URI and a URL is purely in the way its intended to be used. Every URL is a URI, because it Uniquely Identifies a thing. Some URIs are also URLs, because you can Locate things with them. Any URI scheme can be used for a URL, and I know for a fact that you can register handlers for custom URI schemes in at least Windows, Linux, and Android. And on the other hand, http scheme is usually associated with the idea of URL. But e.g. XML namespaces are identified by URIs, often those are http URIs, and there's absolutely no guarantee that the URI can be used to retrieve some document from the Internet.