How to get a list of available `defaults write` terminal commands for OS X El Capitan (expert / superuser) I would like to know where I can find a list of all possible defaults write terminal commands.
(Core OS X related commands, not any due to user installed software.)
Apple themselves must have a manual or technical specification for OS X operating systems and such commands.
Here is an example command (which doesn't work in El Capitan by the way) which demonstrates
defaults write com.apple.driver.AppleBluetoothMultitouch.mouse MouseHorizontalScroll -bool NO

I assume such commands simple write to various configuration files hidden in the OS. It would alternatively be useful to find a document describing all such files and their location on /.
Solution (which was posted in the comments) is defaults read
This is like asking for a list of all possible websites or all possible registry settings. These commands write to Apple and non-Apple software, and will vary depending on the apps/services installed and their versions. 

Since this isn't a single unified settings database, I wouldn't assume Apple maintains a single document or manual on the settings.