Complex sentence: One free initiative is WURFL, which uses a hierarchical XML configuration file mapping hundreds of device capabilities, and a "Wireless Abstraction Layer" called WALL which allows writing tags that are automatically converted into the type of markup supported by the device.
Split into simpler sentences: One free initiative is WURFL, which uses a hierarchical XML configuration file mapping hundreds of device capabilities. WURFL also uses a "Wireless Abstraction Layer", called WALL, which specifies special tags that are automatically converted into a markup language supported by the device.