var ChapterUC = { // single-instance, client-side controller for the MainChapterUC control
    
    // CONSTS
    
    // MEMBERS
        
    onmouseover : function(chapterImage, mainImage) {    
        // on chapter link mouse over, show the chapter image and hide the main image    
        var e = window.event || this.onmouseover.caller.arguments[0];
        var sender = e.srcElement || e.target;
        var lcname = sender.nodeName.toLowerCase();
        
        var img_chapter = document.getElementById(chapterImage);
        var img_mainImage = document.getElementById(mainImage);
            
        img_chapter.style.display='block';
        img_mainImage.style.display='none';

    },
    
    onmouseout : function(chapterImage, mainImage) {    
        // on chapter link mouse out, hide the chapter image and show the main image 
        var e = window.event || this.onmouseout.caller.arguments[0];
        var sender = e.srcElement || e.target;
        var lcname = sender.nodeName.toLowerCase();
        
        var img_chapter = document.getElementById(chapterImage);
        var img_mainImage = document.getElementById(mainImage);
            
        img_chapter.style.display='none';
        img_mainImage.style.display='block';

    },
    
    _end : null
};