1. A computer program product, tangibly embodied in a machine readable storage device, the computer program product comprising instructions operable to cause data processing apparatus to perform operations comprising: parsing a markup-language file to generate a document object model (DOM) hierarchy, wherein the DOM hierarchy defines attributes of a plurality of user interface (UI) elements for rendering a display page through a Web browser; presenting, through the Web browser, the display page including a first UI element of the plurality of UI elements based, at least in part, on the DOM hierarchy locally stored on a client computer, wherein at least a child node of the DOM hierarchy defines one or more attributes of the first UI element; receiving a value from a user of the client computer through the first UI element of the displayed page; in response to at least receiving the value, identifying in the Web browser in the client computer an update to the one or more attributes of the first UI element, wherein the update modifies presentation of the first UI element; determining in the browser whether the update to the one or more attributes of the first UI element can be applied to the locally-stored DOM hierarchy independent of receiving an update to the hierarchy from a server; if the change can be locally applied, automatically modifying the child node in the locally-stored DOM hierarchy, independent of updating the markup-language file, to dynamically update a presentation of the first UI element without re-rendering all of the displayed page; and else, setting a dirty flag.