How to add UserString for a Marker object?

Hi colleagues

I am newbie to ExtendScript So as the title says How to add UserString for a Marker object?

My code is as below, but it does not add UserString to the Markers.

var doc = app.ActiveDoc;

var flow = doc.MainFlowInDoc;

var tbl = 0;

var textItems = flow.GetText(Constants.FTI_MarkerAnchor);

var s = "Number of Comments: " + textItems.len.toString();

alert(s)

for (var i = 0; i < textItems.len; i += 1)

{

    $.write(textItems.obj.MarkerText);

    s = "Comment: " + textItems.obj.MarkerText + " @ " + textItems.obj.TextLoc.offset.toString() + "\n"
        + textItems.obj.Unique;

    GetUniqueObject(textItems.obj.Unique).UserString = "Added by Dan"; // Will add more useful data here

}