script help

[fbig22]

I'm studying some javascript code specified for cpm. Although this is not my code I'm just trying to understand all the aspects of the code. Some of these lines are confusing to me and I'm unsure of the exact purpose. any info on these codes would be much appreciated. The code I'm unsure about will be highlighted in bold. Thanks again.

ps: I'm mostly confused on the purpose of hstnam and servUrl within the code. What is it's purpose. Is it to collect the host name and server URL of the website that has the code or what? Sorry if its a dumb question. Thanks.

var GALAXY = new GALAXYcontrolObject();
window.onerror = new function() { return true; }
function GALAXYcontrolObject() {
  this.adNum = 0;
  this.DisplayHTML = GALAXYcontrolObject_DisplayHTML;
  this.DisplayXhtml = GALAXYcontrolObject_DisplayXhtml;
  this.DisplayBanner = GALAXYcontrolObject_DisplayBanner; }
[B]function GALAXYcontrolObject_DisplayHTML( hstNam, servUrl ) {
  this.adNum++;
  servUrl = 'http://'+hstNam+'.mtree.com'+servUrl;
  var d = document;[/B]
  if( d.layers ) {
    var opts = "WIDTH=600 HEIGHT=150 BORDER=0" ;
    d.writeln('<ILAYER SRC="'+servUrl+'" '+opts+'></ILAYER>');
  } [B]else if( d.all ) {
    servUrl += 'type_1/func_GalaxyDisplayHtml'+this.adNum+'/';
    d.writeln('<'+'SCRIPT LANGUAGE="JavaScript" SRC="'+servUrl+
	      '"></'+'SCRIPT>');[/B]