function parse_form_data(data_name) {
  var query=location.search;
  if (query!="") {
    var pos0=1;
    var next=true;
    var paar="";
    var k="";
    var v="";
    var wert="";
    // Erstes Schlüssel-Wert-Paar suchen
    var pos1=query.indexOf(";",pos0);
    var trennzeichen = ';';
    if (pos1 >= 0)
    {
      trennzeichen = ';';
    }
    else
    {
      pos1=query.indexOf("&",pos0);
      if (pos1 >= 0)
      {
        trennzeichen = '&';
      }
    }
    if (pos1<0) 
    {
      pos1=query.length;
    }
    
    while (next) 
    {
      // Paar ausschneiden
      paar=query.substring(pos0, pos1);
      // In Schlüssel und Wert zerlegen
      k=paar.substring(0, paar.indexOf("=",0));
      v=paar.substring(paar.indexOf("=",0)+1,paar.length);
      // Falls gesuchter Name gleich Schlüssel
      if (k==data_name) 
      {
        next=false;
        wert=unescape(v);
      } 
      else 
      {
        pos0=pos1+1;
        if (pos0 > query.length)
        {
          next=false;
        }
        
        pos1=query.indexOf(trennzeichen,pos0);
        if (pos1<0) 
        {
          pos1=query.length;
        }
      }
    }
    return wert;
  } 
  else 
  {
    return "";
  }
  
}