1. A method of controlling user interface features of a web application, the method comprising the steps of: describing the web application using a presentation markup language that has been extended to include a collection of user interface control elements to create an extended presentation markup language, the web application description including a user interface control comprising a name element for associating the user interface control of the web application with a user interface control element of the collection of user interface control elements; searching, in a document object model (DOM) of the web application, for user interface controls of the web application, each user interface control identified by a namespace associated with user interface control elements of the collection of user interface control elements included in the extended presentation markup language, the namespace including a prefix identifying the collection of user interface control elements as part of the extended presentation markup language and allowing a presentation markup language parser to identify them as part of the DOM; for each located user interface control; generating a function name for the located user interface control element following a predetermined naming convention comprising adding the prefix to a unique name associated with the located user interface control element; calling a predetermined set of user interface control instructions associated with the located user interface control element using the generated function name, the predetermined set of user interface control instructions defining the behavior of the located user interface control element and comprising a first portion relating uniquely to the located user interface control element, a second portion commonly relating to multiple user interface control elements, and an attribute relating to a skin template controlling the display of the located user interface control; and rendering the DOM of the web application described in the extended presentation markup language, including rendering the located user interface control of the web application based on at least the predetermined set of user interface control instructions.