"Zoom in" to a render extent

Currently, you can create multiple render extents, one useful purpose of which is being able to examine smaller areas of a large world in greater detail.

However, it is cumbersome to manage this. It would be helpful if there was a "zoom into" button that let you select an area of a render extent to temporarily view and work within for detailing. When unchecked, it would revert back to showing the full render extent.