Instructors can enrich textbooks through the use of overlays. Overlays are links to extra learning content.  They are visible on the page via an icon and can be clicked to display their content. 

Each type of overlay is represented by an icon: 

If you hover your mouse over an overlay icon, you will see the name of the enrichment attached to it:

To see the content of the overlay, click on the overlay icon: 

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