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 the LWJGL AppletLoader in the HTML code of. It is used to specify a unique version for each jar file to cache them for re-use. If the stored al_version matches the latest jar file, that jar file is re-used; otherwise a new jar is downloaded.