Answer - The XHTML modularization model defines the modules of XHTML. XHTML is a simple, but large language. XHTML contains most of the functionality a web developer will need. For some purposes XHTML is too large and complex, and for other purposes it is much too simple. By splitting XHTML into modules, the W3C (World Wide web Consortium) has created small and well-defined sets of XHTML elements that can be used separately for simple devices as well as combined with other XML standards into larger and more complex applications. With modular XHTML, product and application designers can: * Choose the elements to be supported by a device using standard XHTML building blocks. * Add extensions to XHTML, using XML, without breaking the XHTML standard. * Simplify XHTML for devices like hand held computers, mobile phones, TV, and home appliances. * Extend XHTML for complex applications by adding new XML functionality (like MathML, SVG, Voice and Multimedia). * Define XHTML profiles like XHTML Basic (a subset of XHTML for mobile devices).