JavaScript Tab Inserts Tab / How To Insert An Actual Tab in an Input or Textarea

<textarea cols="50" onkeydown="return interceptTabs(event,this);" rows="15"></textarea>

function interceptTabs(evt,control){
    key=evt.keyCode?evt.keyCode:evt.which?evt.which:evt.charCode;
    if(key==9){
        insertAtCursor(control,'t');
        return false;
    }
    else{
        return key;
    }
}
function insertAtCursor(myField, myValue){
    if(document.selection){
        /* ie */
        myField.focus();
        sel=document.selection.createRange();
        sel.text=myValue;
    }
    else if(myField.selectionStart||myField.selectionStart=='0'){
        /* mozilla support */
        var startPos=myField.selectionStart;
        var endPos=myField.selectionEnd;
        restoreTop=myField.scrollTop;
        myField.value=myField.value.substring(0,startPos)+myValue+myField.value.substring(endPos,myField.value.length);
        myField.selectionStart=startPos+myValue.length;
        myField.selectionEnd=startPos+myValue.length;
        if(restoreTop>0){
            myField.scrollTop=restoreTop;
        }
    }
    else{
        myField.value+=myValue;
    }
}