How to use Extra Card Detail?

What’s an example of a the power up Extra Card Detail?

Also, where can I find definitions of these Power up rems? Extra Card Detail does not show up in a list from a website.

Add a child to any rem that is a flashcard, i.e. that is either in the front::back format or has a cloze deletion inside it (including image occlusions), tag that child as extra card detail. Whenever you answer that flashcard in the queue, the child will be shown.
image
image
image

The reference for all powerups can be found here.