function roll_over(img_name, img_src) {
    document[img_name].src = img_src;
}

String.prototype.trim = function() {
    return (this.replace(/^[\s\xA0]+/, "").replace(/[\s\xA0]+$/, ""))
}

String.prototype.startsWith = function(str) {
    return (this.match("^" + str) == str) 
}

String.prototype.endsWith = function(str) {
    return (this.match(str + "$") == str) 
}