code: function(nBorderWidth) {
      var aLastHeaders = this._oColumnSet.headers[this._oColumnSet.headers.length-1] || [],
          len = aLastHeaders.length,
          sPrefix = this._sId+"-fixedth-",
          sValue = nBorderWidth + "px solid " + this.get("COLOR_COLUMNFILLER");
  
      this._elThead.style.display = "none";
      for(var i=0; i<len; i++) {
          Dom.get(sPrefix+aLastHeaders[i]).style.borderRight = sValue;
      }
      this._elThead.style.display = "";
  }
docs: Sets Column header overhang to given width.
  
  @method _setOverhangValue
  @param nBorderWidth {Number} Value of new border for overhang.
  @private