An infrastructure is provided for creating applications for mobile information devices, using a tag-based markup language, MIDML. Applications are defined based on easily manipulated textual tags, without need for writing specific code. The tags are processed to ultimately generate source code files. Initially, the input is parsed. Next, a hierarchical object model of the application is populated with objects. Separate readers read and parse the different tags and accompanying elements. The readers are registered in a descriptor object factory, to be instantiated as required in processing extended MIDML files. The object model enables the capabilities of the system to be easily extended, simply by adding new tags, and readers to the existing factory set. The resulting object model is accessible to a generator that produces the actual output.