When multiple assets are similar to each other, you can “stack” them so that you can keep them together. For example, if you upload a JPG, PNG, and PSD of the same image, you can stack these assets so that you can easily find and edit that set of assets all at once. A set of stacked assets is called a “Stack.” When you stack assets, you pick which asset you want to represent the other assets. This becomes the “Lead Asset,” which is shown as the “top” asset of the Stack. The other assets in the Stack are “Alternative Versions” of the Lead Asset. A Stack creates a parent/child relationship between the assets. The Lead Asset is the parent, and the Alternative Versions are the child assets. If users want to see all assets in a Stack in the search results, they can deploy (expand) the Stacks.
Feature Documentation: Stacks
Security Function
Stacking and unstacking assets requires the Stack Documents Security Function.