Exponent ships with and makes great use of the YAHOO! User Interface (YUI) Javascript and CSS library. Core Exponent Developers keep a close eye on YUI as they make heavier use of the library, integrating more of its components into the system, while dropping other 3rd party systems. The idea is to get Exponent down to as few dependencies as possible. Exponent 0.97 ships with YUI 2.5.2.