[msufx]

function createLink() {
  if (!validateMode()) return;
 
  var isA = getEl("A",document.getElementById('Composition')[].contentWindow.selection.createRange().parentElement());
  var str=prompt("Введите адрес:", isA ? isA.href : "http:\/\/");
 
  if ((str!=null) && (str!="http://")) {
    if (document.getElementById('Composition')[].contentWindow.selection.type=="None") {
      Composition.focus();
      var sel=document.getElementById('Composition')[].contentWindow.selection.createRange();
      sel.pasteHTML("<A HREF=\""+str+"\">"+str+"</A> ");
      sel.select();
    }
    else formatC("CreateLink",str);
  }
  else document.getElementById('Composition')[].focus();
}
 
function createBR() {
  if (!validateMode()) return;
  var sel=document.getElementById('Composition').selection.createRange();
      sel.pasteHTML("<br>");
      sel.select();
 Composition.focus();
}

<table border="1" cellpadding="0" cellspacing="0" width="100%" bordercolor='#C0C0C0' bordercolordark='#FFFFFF'><tr><td>
<IFRAME class=Composition id=Composition width="100%" height=400 frameborder=0 name="Composition">
</IFRAME>
</td></tr></table>

Пробовал менять

Composition.document.selection.createRange();

на

document.getElementById('Composition').selection.c reateRange();

Результата ни какого.