This question has a template already created for answering it. That is, instead of the answer textbox starting out empty, it starts out with this text in it:
[![Tagline to show on mouseover]] : http://image-url : http://clickthrough-url
Now, granted, a template like this would rarely be suitable...especially outside of
meta. But...how is that done? Is this just a special feature that only moderators or Stack Exchange employees can use?