What Does gs_upl in the URL mean?

Question

In any of the google search URL's what does gs_upl mean ?
for example:
http://www.google.com/search?hl=en&source=hp&biw=1366&bih=667&q=stack+overflow&oq=stac&aq=1&aqi=g10&aql=&gs_sm=e&gs_upl=1045l1663l0l3648l4l4l0l0l0l0l258l682l0.3.1l4l0
So what does gs_upl=1045l1663l0l3648l4l4l0l0l0l0l258l682l0.3.1l4l0 mean here ?

Answer 1

From the script that builds gs_upl (j) I found that:

function(){
   var b=a.R(),e="f";f.md()?e="o":d.na()&&(e=d.gf());
   var j="",o=f.sa();o&&(j=o.Ub());var l="";
   if(o=d.K()){
      for(var l={zd:[],$b:v,Ja:0},r=o.length,t=0,w;t<r;++t){
           w=t==r-1;var y=o[t],u=l,z=i.za(y.F()).Ha();(y=y.Wa())&&(z+="-"+y);
           if(z!=u.$b)
              u.Ja&&u.zd.push(u.$b,u.Ja),u.Ja=0,u.$b=z;
              ++u.Ja;w&&u.Ja&&u.zd.push(u.$b,u.Ja)}l=l.zd.join("")
      }
      b={oq:b,aq:e,aqi:l,aql:j
   }
   ;
   if(g.ub)
     j=Z()-q,
     j[c(a.Te()),c(a.Ue()),k,j,h.Of(),h.Nf(),h.dd(),h.ed(),
       h.Kf(),h.Mf(),h.Lf(),h.Qf(),h.Jf(),h.Pf(),c(a.Ve())]
       .join("l"),
   b.gs_upl=j;
   return b
}