The Yahoo! User Interface (YUI) Library is a set of utilities and controls, written in JavaScript, for building richly interactive web applications using techniques such as DOM scripting, DHTML and AJAX.
http://developer.yahoo.com/yui/
JavaScript Libraries and Functions · JavaScript Library
Get access to data on 5,996,484 websites that are Yahoo User Interface Customers. We know of 2,396,814 live websites using Yahoo User Interface and an additional 3,599,670 sites that used Yahoo User Interface historically and 1,717,197 websites in the United States.
Get a list of 5,996,484 websites using Yahoo User Interface which includes location information, hosting data, contact details, 2,396,814 currently live websites and an additional 1,465,297 domains that redirect to sites in this list. 3,599,670 sites that used this technology previously and 1,717,197 websites in the United States currently using Yahoo User Interface.