BB-kod (ändra markerad text) ?

Är tacksam ifall någon kunde hjälpa mig att ändra följande kod så att det fungerar att ändra markerad text.

Har förstått att man ska använda sig av "insertAroundCursor", men förstår inte riktigt hur jag ska ändra koden nedan.

<script language=javascript>
function insertAtCursor(myField, myValue) {
//IE support
  if (document.selection) {
    myField.focus();
    sel = document.selection.createRange();
    sel.text = myValue;
  }

//MOZILLA/NETSCAPE support
  else if (myField.selectionStart || myField.selectionStart == '0') {
    var startPos = myField.selectionStart;
    var endPos = myField.selectionEnd;
    myField.value = myField.value.substring(0, startPos) + myValue + myField.value.substring(endPos, myField.value.length);
    myField.selectionEnd = startPos + myValue.length;
  } else {
    myField.value += myValue;
  }
  myField.focus();
}

// calling the function
function SmileIT(smile,form,text){
    insertAtCursor(document.forms[form].elements[text], smile)
}

function BBTag(tag,s,text,form){
  var df  = document.forms[form].elements[s];
  var ele = document.forms[form].elements[text];
  var tval;
  var ttag;
  switch(tag) {
    case '[quote]':
            tval = "QUOTE ";
            ttag  = "[/quote]";
            if(df.value == "QUOTE ") {
              tval = "QUOTE*";
              ttag  = "[quote]";
            }
            break;
    case '[img]':
            tval = "IMG ";
            ttag = "[/img]";
            if(df.value == "IMG ") {
              tval = "IMG*";
              ttag  = "[img]";
            }
            break;

    case '[url]':
            tval = "URL ";
            ttag = "[/url]";
            if(df.value == "URL ") {
              tval = "URL*";
              ttag  = "[url]";
            }
            break;

    case '[*]':
            tval= "List ";
                        if(df.value == "List ") ttag  = "[*]";
            break;

            insertAtCursor(ele, tag);
            df.elements[s].value = tval;
            break;

    case '[hr]':
                        tval= "Hr ";
                        if(df.value =="HR "){
                            ttag="[HR]";
            }
                        insertAtCursor(ele,tag);
            df.elements[s].value=tval;
            break;

    case '[center]':    tval= "Center";
            ttag= "[/center]";
            if(df.value == "Center "){
                    tval = "Center* ";
                 ttag="[center]";
                }
                    
                   
            break;            

    case '[b]':
            tval = "B ";
            ttag = "[/b]";
            if(df.value == "B ") {
              tval = "B*";
              ttag  = "[b]";
            }
            break;

    case '[i]':
            tval = "I ";
            ttag = "[/i]";
            if(df.value == "I ") {
              tval = "I*";
              ttag  = "[i]";
            }
            break;

    case '[u]':
            tval = "U ";
            ttag = "[/u]";
            if(df.value == "U ") {
              tval = "U*";
              ttag  = "[u]";
            }
            break;

    case '[s]':
            tval = "S ";
            ttag = "[/s]";
            if(df.value == "S ") {
              tval = "S*";
              ttag  = "[s]";
            }
            break;
  }
  if(tval!="") df.value = tval;
  if(ttag!="") insertAtCursor(ele, ttag);
}

</script>

      <table cellpadding="2" cellspacing="1">
      <tr>
      <td class=embedded><input style="font-weight: bold;" type="button" name="bold" value="B " onclick="javascript: BBTag('[b]','bold','<? echo $name; ?>','<? echo $form; ?>')" /></td>
      <td class=embedded><input style="font-style: italic;" type="button" name="italic" value="I " onclick="javascript: BBTag('[i]','italic','<? echo $name; ?>','<? echo $form; ?>')" /></td>
      <td class=embedded><input style="text-decoration: underline;" type="button" name="underline" value="U " onclick="javascript: BBTag('[u]','underline','<? echo $name; ?>','<? echo $form; ?>')" /></td>
      <td class=embedded><input style="text-decoration: stroke;" type="button" name="stroke" value="S " onclick="javascript: BBTag('[s]','stroke','<? echo $name; ?>','<? echo $form; ?>')" /></td>
      <td class=embedded><input type="button" name="li" value="List " onclick="javascript: BBTag('[*]','li','<? echo $name; ?>','<? echo $form; ?>')" /></td>
      <td class=embedded><input type="button" name="quote" value="QUOTE " onclick="javascript: BBTag('[quote]','quote','<? echo $name; ?>','<? echo $form; ?>')" /></td>
      <td class=embedded><input type="button" name="url" value="URL " onclick="javascript: BBTag('[url]','url','<? echo $name; ?>','<? echo $form; ?>')" /></td>
      <td class=embedded><input type="button" name="img" value="IMG " onclick="javascript: BBTag('[img]','img','<? echo $name; ?>','<? echo $form; ?>')" /></td>
      <td class=embedded><input type="button" name="hr" value="HR " onclick="javascript: BBTag('[hr]','hr','<? echo $name; ?>','<? echo $form; ?>')" /></td>
      <td class=embedded><input type="button" name="center" value="Center " onclick="javascript: BBTag('[center]','center','<? echo $name; ?>','<? echo $form; ?>')" /></td>
      <td class=embedded>&nbsp;<a href="javascript: PopMoreTags('<? echo $form; ?>','<? echo $name; ?>')">Fler koder</a></td>
      </tr>
      </table>