Al version

al_version (AppletLoader version) is a number used in versions prior to Java Edition Alpha to uniquely identify a client version of the game.

Usage
al_version is a positive floating-point number given as a parameter to a website applet that tells the LWJGL AppletLoader which applet version shall be loaded to the website as the current version. It is used to cache jar files for reuse; when al_version changes, a new jar is downloaded.