======== Modeling ======== Introduction ------------ MuJoCo's native model format is **MJCF**, an XML-based language designed to describe complex dynamical systems. This chapter is the primary MJCF modeling guide. The complete element and attribute reference manual is available in the :doc:`XMLreference` chapter. MuJoCo also supports loading models from other formats such as URDF (see :ref:`URDF extensions `), MJZ Zip archives (see :ref:`MJZ Archives `), and OpenUSD (see :doc:`OpenUSD/index`). MJCF models can represent complex dynamical systems with a wide range of features and model elements. Accessing all these features requires a rich modeling format, which can become cumbersome if it is not designed with usability in mind. Therefore we have made an effort to design MJCF as a scalable format, allowing users to start small and build more detailed models later. Particularly helpful in this regard is the extensive :ref:`default setting ` mechanism inspired by the idea of Cascading Style Sheets (CSS) inlined in HTML. It enables users to rapidly create new models and experiment with them. Experimentation is further aided by numerous :ref:`options