The Open Source mobility middleware developed in the Fuego Core project provides a stack for efficient XML processing on limited devices. Its components are a persistent map API, advanced XML serialization and out-of-order parsing with byte-level access (XAS), data structures and algorithms for lazy manipulation and random access to XML trees (RefTree), and a component for XML document management (RAXS) such as packaging, versioning, and synchronization. The components provide a toolbox of simple and lightweight XML processing techniques rather than a complete XML database. We demonstrate the Fuego XML stack by building a viewer and multiversion editor capable of processing gigabyte-sized Wikipedia XML files on a mobile phone. We present performance measurements obtained on the phone, and a comparison to implementations based on existing technologies. These show that the Fuego XML stack allows going beyond what is commonly considered feasible on limited devices in terms of XML proces...