Of course you could actually enable the option to understand the behavior thoroughly && firsthand but maybe a better description would be helpful as well:
in reply to Null Voting--or Undef Voting?
in thread Trinary Voting
The null option provides another voting option (in addition to the default ++ && --) for each node. This new option is labeled +=0 && actually exists as a "checked" radio button within the HTML so when you accidentally select a value altering vote option, you are free to re-select the default +=0 radio button so that no vote (on that node) will be cast when you proceed to the "vote" stumbit button. =)
Hope that helps a bit. I remember asking for this feature way back when... gosh... that must have been like 6 months ago. Sheesh. I still find it mighty handy. TTFN.
p.s. Byslexia is a Ditch!