whats wrong withat ref: window.frames["ifrm_3"].contentDocument.body.style.fontSize ?

[geotsa]

what's wrong with that ref: window.frames["ifrm_3"].contentDocument.body.style.fontSize ?
I thought it would be similar to that:
document.body.style.fontSize

Or else this works

<script language="javascript">
function resizeText(af3isi) 
{var size=parseFloat(window.frames["iframe_3"].contentDocument.body.style.fontSize)
 if(size>8 && size<18)
   {    Document.body.style.fontSize= parseFloat(Document.body.style.fontSize) + (af3isi) + "px";
   }
 else if (size<=8)
   {
       if(af3isi<0)
         {
             Document.body.style.fontSize=10+(af3isi)+"px"
         }
       else
         {
             Document.body.style.fontSize=8+(af3isi)+"px"
         }
   }
 else
   {
      if(af3isi>0)
        {
            Document.body.style.fontSize=16+(af3isi)+"px"
        }
      else
        {
            Document.body.style.fontSize=18+(af3isi)+"px"
        }
   }
}
</script>

but this doesn't

<script language="javascript">
function resizeText(af3isi) 
{var size=parseFloat(window.frames["iframe_3"].contentDocument.body.style.fontSize)
 if(size>8 && size<18)
   {    window.frames["iframe_3"].contentDocument.body.style.fontSize= parseFloat(window.frames["iframe_3"].contentDocument.body.style.fontSize) + (af3isi) + "px";
   }
 else if (size<=8)
   {
       if(af3isi<0)
         {
             window.frames["iframe_3"].contentDocument.body.style.fontSize=10+(af3isi)+"px"
         }
       else
         {
             window.frames["iframe_3"].contentDocument.body.style.fontSize=8+(af3isi)+"px"
         }
   }
 else
   {
      if(af3isi>0)
        {
            window.frames["iframe_3"].contentDocument.body.style.fontSize=16+(af3isi)+"px"
        }
      else
        {
            window.frames["iframe_3"].contentDocument.body.style.fontSize=18+(af3isi)+"px"
        }
   }
}
</script>