preferences.txt switches are not documented

I was browsing through the net for explanation of what switches are possible and how they behave. Found no site where it is described what the switches/options under preferences.txt are doing.

Start by locating preferences.txt and inventorying the switches and options it contains. Review the existing docs structure on docs.arduino.cc to find the appropriate page or section. Done means every relevant switch has a clear explanation of its behavior and the documentation is published in the expected location.

Written by the indexing model from the issue text.