To be clear, the difference is that an URI generally only allows you to refer to a resource ("Identifier"), whereas an URL also tells you where to find and acce

To be clear, the difference is that an URI generally only allows you to refer to a resource ("Identifier"), whereas an URL also tells you where to find and access it ("Locator"). For instance, `https://example.com/foo` https://example.com/foo` tells you that the resource can be accessed via the HTTPS protocol, at the server with the hostname example.com (on port 443), by asking it for the path `/foo`. It is hence an URL. On the other hand, `isbn:123456789012` precisely identifies a specific book, but gives you no information about how to locate it. Thus, it is just an URI, not an URL. (Every URL is also an URI, though.)