The DOM Environment supports two types of profiles - one stictly for models (Model profile) and one that is either directly inserted into HTML or exists as a stand-alone file. Profiles that operate in the Classic Environment may be supported by the browser to the extent that they conform to the DOM Envirnoment. The HTML profile is a proper superset of the Model profile - every node in the Model profile is in the HTML profile and the HTML profile contains nodes that are not in the Model profile. Each profile allows a number of extensions to support different capabilities. If a browser supports an extension for the Model profile, it shall support the same extension for the HTML profile.