Official documentation of synclient parameters

Found it:

http://www.x.org/archive/X11R7.5/doc/man/man4/synaptics.4.html

Thanks to @Rinzwind for the link to synclient man page.

Manual page from x.org. So that might be the official documentation though it is a manual styled one so it will be the same information if you type man synclient.

The arch website has a very thorough documentation: Touchpad_Synaptics

And the command itself will list all user options with:

synclient -l

Regarding: "TouchpadOff=2" in comments: The arch website has a section "Software toggle" that seems to indicate it has a 0 and 1 as options; not a 2.

edit: I also found this script:

#!/bin/bash
# touchpad-off - bash script to turn the synaptics touch pad off

# synclient TouchpadOff=1
# Alternatively, only disable scrolling and tapping
synclient TouchpadOff=2

But I have not found any official reference on this...

So it seems your question is not that odd ;)