code: function doGetCaretPosition(oField) {
      var iCaretPos = 0;
      if (document.selection) {
        oField.focus ();
        var oSel = document.selection.createRange();
        oSel.moveStart ('character', -oField.value.length);
        iCaretPos = oSel.text.length;
      } else if (oField.selectionStart || oField.selectionStart == '0') {
        iCaretPos = oField.selectionStart;
      }
      return (iCaretPos);
    }
docs: Returns the position of the caret in the given input field
  http://flightschool.acylt.com/devnotes/caret-position-woes/