This command uses what the WMO calls "Coordinate descriptors" to create new arrays (lists) in the JSON format. See section 3.1.2.2 of the WMO BUFR guide:
https://www.wmo.int/pages/prog/www/WDM/Guides/BUFRCREX-Layer3-English-only.pdf
This means we create a new JSON list/array for descriptors in classes 00 to 09. For other descriptors, we stay in the same list/array. When a descriptor from class 00 to 09 re-appears, we close all the lists/arrays up to the previous occurrence of the same descriptor.