This command enables and disables (toggles) the clearing of collision boxes after every frame - meaning when enabled, collision boxes from previous frames will stay on the screen. For example, if an NPC is moving, the collision boxes from its previous positions will stay visible until this setting is toggled off. Note that you need boxes toggled on in order for this command to have any effect.
The syntax for the clearboxes command is as follows:
/clearboxes Debug Mode
Find below working examples of the clearboxes command.
This is the only way the clear boxes command can be executed. It is a toggle command meaning if this setting is disabled, running this command will enable it, otherwise (if the setting is already enabled), running this command will disable it.