- An app: URL is a [[!URL]] that can be used by a packaged - application to address resources within its container (e.g., a .zip - file). + An app: URL is a [[!URL]] whose scheme component + is `app` (case-insensitive) and whose host component is an + instance identifier. A user agent can use app: URLs to obtain + resources from within a packaged application (e.g., a .zip file).
++ Traditionally, the syntax of [[URI]]s were represented using [[ABNF]]. + However, as few ever implemented ABNF parsers, validators, or + producers, and given how complicated [[ABNF]] is to decypher, it + turned out not to be very helpful to implemeters or readers. So, + nowawadays, we just restrict certain parts of the URL to values and + let the URL + parser spit out the right result. +
++ For readers accustomed to seeing [[ABNF]] syntax representations of + [[URI]]s, the app URL would look like this: +
++ appurl = "app":" hier-part [ "?" query ] [ "#" fragment ] ++
+ The [[URI]] specification defines what each component in the above [[ABNF]] means. +
+