Scripting with bridge

Hello Muppet Mark.

We are using CS 5.5

Here is the sample code, as found in the sdk(but some little test modifications by me), copyright adobe

The script is working correct, but i am trying to understand how it does what it does.

#target bridge
#targetengine "MainEngine"
function SnpSaveAsJPEG()
{
    //The context in which this snippet can run.
     //type String
    this.requiredContext = "\tExecute against Bridge.\nBridge must be running and \n" 
        + "at least one thumbnail selected that is not a folder.";
    $.level = 1; // Debugging level
}
/**
 Functional part of this snippet.  
 Gets a File object for each selected thumbnail, and uses it to
 create a BitmapData object. Uses the BitmapData object to export
 to the JPEG format.
     @return True if the snippet ran as expected, false if no files are selected in Bridge
     @type Boolean
*/
SnpSaveAsJPEG.prototype.run = function()
{
    var retval = true;
    if(!this.canRun()) {
        retval = false;    
        return retval;
    }
    // Get the selected Thumbnail objects - only accept these file types
    var thumbs = app.document.getSelection("ai");
    // Go through each of the selected thumbnails
    if(thumbs.length != 0)
    {
        for(var i = 0;i < thumbs.length;i++)
        {
            // get associated File object, ignore folders
            if(thumbs.spec instanceof File)
            {
                var thumb = thumbs;
                // create a BitmapData object
                var bm = new BitmapData(thumbs.spec);
                if(bm instanceof BitmapData)
                {
                    // create the path and file name
                    var exportFilePath = thumbs.parent.spec + "/SnpSaveAsJPEG_" + thumbs.name + ".jpg";
                    // create the new file and export the data
                    bm.exportTo(new File(exportFilePath));
                }
            }
        }
    }
    else
    {
        retval = false;
    }
    return retval;
}
/**
 Determines whether snippet can be run given current context.  The snippet will
 fail if these preconditions are not met: 
 <ul>
 <li> Must in Bridge
 <li> At least one file must be selected in Bridge
 </ul>
 @return True if this snippet can run, false otherwise
 @type boolean
*/
SnpSaveAsJPEG.prototype.canRun = function()
{    
    // must run in Bridge 
    // must be at least one selection. 
    if((BridgeTalk.appName == "bridge") && (app.document.selectionLength > 0)) 
    {
        return true;
    }
    // Fail if these preconditions are not met.  
    $.writeln("ERROR:: Cannot run SnpSaveAsJPEG");
    $.writeln(this.requiredContext);
    return false;
}
/**
 "main program": construct an anonymous instance and run it
  as long as we are not unit-testing this snippet.
*/
//if(typeof(SnpSaveAsJPEG_unitTest)  == "undefined") {
//    new SnpSaveAsJPEG().run();
//}
new SnpSaveAsJPEG().run();