[maybe off-topic] difference between IsEnabled and ScreenReaderEnabled DBus properties

Hello,

I post both to Orca and Debian-Accessibility lists because I am not sure 
about which one is the most related.

I see there are two properties in org.a11y.Status (DBUS):
* IsEnabled (which is enabled by Orca on startup
* ScreenReaderEnabled (which is only checked but not set by Orca)

What is the difference between these?
Why only managing the most generic and not the specific one for screen 
reader?

It looks if we want to check if a screen reader is enabled, we have to 
check if something related to accessibility is enabled?

Thanks and best regards,

-- 
Patrick ZAJDA