Union Transformations?

In a comment to my previous entry, Divya asked me to check out an Informatica quiz here: http://tinyurl.com/infaquiz

Tough quiz. Some of the questions were pretty tough. One in particular threw me for a loop - one about Union transformations.

While trying to answer it, it occurred to me that I had no idea what a Union transformation was. After the quiz, I pulled up Informatica's help on this topic, and found Union Transformation in the help, but couldn't actually add one to any mapping.

I found this:
To create a Union transformation:
1. In the Mapping Designer, click Transformations > Create.
2. Select Union Transformation and enter the name of the transformation.
...

Except that when I try step 2, I fail - because Union Transformation isn't a choice for me in my drop-down. Anyone have any idea what is going on here? Is this a transformation that doesn't come with all default installations of Informatica?