Webtrends Analytics 9 Adminstration Guide, November 2012
If you use Webtrends Analytics 9 or the SmartSource Data Collector, the wt.dl parameter can be passed to the data collection server using a META tag or ActionScript. However, the recommended method for enabling wt.dl tracking is to implement Event Tracking using the Webtrends Tag Builder at tagbuilder.webtrends.com. wt.dl can be passed to dcsMultiTrack.
If you did not create your tags using the Tag Builder, you can learn about tracking complex web page interactions using dcsMultiTrack.