Pop Up for TNEW

Hello,

I have been trying to add a pop up (or a modal window?) with basic HTML in TNEW, hopefully on the event descriptions.  However, I can't find code using HTML only.  Has anyone found a way to do this, or can point to a good example?  We currently have a pop-out browser, but we were hoping to have a window pop up within the same browser.

Thanks so much!

Andrew