Sabre merge method
Sabre is a merge method created by Google that improves photo quality on some modes. Some call it "super resolution" because of the sharpness/detail improvements. It's used by Google for Night Sight, but some GCam mods also use it for zoomed photos and HDR+ Enhanced. Works with the RAW10 format (other RAW formats may result in black photos).
Some versions come with a DCI-P3 option. On phones with displays that support DCI-P3, it should result in photos with more vibrant colours.
To learn more about this colour space, check the wikipedia page about DCI-P3.
ZSL = zero shooting lag
means you won't get camera freeze after taking a HDR+ auto shoot. It is build-in the Google Camera 4.2 and only works on Pixel phones.
I started to collect information about the settings but as you see it's still on going ... but will be continued by time.
to all: more input from members appreciated so we maybe end up with a full description of what you can do and what is the benefit of it