Split callbacks is an alternative operating view to the main active callbacks page.
This method aligns the interactive view vertically instead of horizontally and allows you to have multiple full callbacks in view at once. This makes it easy to look at the output of one callback while typing into another callback.
From the main callback screen, click the dropdown for a callback and select "Expand Callback". This will open a new tab with a split callback for just that callback.
By selecting another callback at the top and selecting "Add Callback", more vertical callbacks can be brought into view:
Callbacks are always ordered sequentially and you can simply click the red X next to the callback to remove it from this screen (it does not mark it as inactive).