Project Creators can embed references within Text passages pointing to uploaded Resources. Gray boxes within a Text indicate places where a Resource has been added to the Text. When reading, you can click on the box or its corresponding thumbnail in the left margin, or at the bottom of the screen if you are on a mobile device, to open the Resource and access its page within Manifold.
In the screenshot above, you can see where the author has embedded three resources within a Text. When you hover over the third resource (that is, the third gray cube), the thumbnail for the embedded Resource will appear to the left of the Text and the cube will turn green, as shown below:
