How to Work With Nested Slide Layouts in Droppable Zones
This functionality is only available for Slides and Brief document types.
Many Slide layouts allow users to add other layouts within.
This allows for a variety of designs and flexibility,
In the example below, you see a basic slide structure in which 3 other layouts are added.

When Layouts are added to dropzones, they become nested.
In the example used below we have a basic slide with two columns. The left column has one child layout and the right column has two child layouts.

You can drill into the structure by using the Fields menu. Doing so will show you the elements that are inside the children and you can show and hide the ones needed. Click on the back chevron icon to go back to the parent layout.