title: Is there a good reference guide for deciphering http user-agent strings?
body: <p>We're getting some odd errors reported on our website, and are trying to find out some details on who is doing the looking.  I'm looking at a sample user-agent strings and seeing things like:</p>
  
  <p>Mozilla/5.0 (Windows; U; Windows NT6.0; en-US; rv:1.9.0.6) Gecko/2009011913 Firefox/3.0.6</p>
  
  <p>Now some of this is obvious, but some of it is less so ("U"?)  From the pattern of the hits, I'd suspect that this was a robot, but I don't see anything that I recognize in this string to clue me in to that.  I'd like to know what some of the things in this (and other different) strings mean.  Is there a comprehensive reference somewhere?</p>