Many openstack client commands (in particular the list type commands) have a -c option by which the displayed columns can be selected. I have, however, not found what columns are valid. Recent example:

$ openstack hypervisor list -c id -c free_disk_gb 
No recognized column names in [u'id', u'free_disk_gb']

Although these columns exist:

$ openstack hypervisor show 1 | grep -e id -e free_disk_gb
| free_disk_gb         | 52                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                            
| id                   | 1

(output shortened)

Are the valid columns documented somewhere, or is there a command that tells me what columns are available?