arcgis server - Passing GPString value via Flex

In this example from the ArcGIS for Flex samples page: Clip and Ship

I am curious how from this function how the label property of each check box that is passed as input for the Layers_to_Clip parameter of the GPService are interpreted by the GPService as actual pieces of data.

private function getLayersToClip():Array
        {
            var layersToClip:Array = [];

            if (incidentPointsCheckBox.selected)
            {
                layersToClip.push(incidentPointsCheckBox.label);
            }
            if (incidentLinesCheckBox.selected)

            {
                layersToClip.push(incidentLinesCheckBox.label);
            }
            if (incidentAreaCheckBox.selected)
            {
                layersToClip.push(incidentAreaCheckBox.label);
            }

            return layersToClip;
        }

I have looked at the Clip and Ship data from the ArcTutor files and don't understand how the GPString values - which in this case are "Input Incident Points", "Input Incident Polylines", and "Input Incident Polygons" - correspond to any of the map layers.

Part 2) Ideally I would like to change my Flex application to take items selected from checkboxes and pass them into my model in the same fashion, except I won't be extracting them but using them in analysis. If preprocessing is done, every input would be a raster dataset regardless of the original geometry and the output would be a raster as well. How can I have those checkboxes refer to selected input rasters in a database location or within the map document/gp service?

Thanks in advance, I've been banging my head against the wall with this one,

Sean