function DialogOverlay(content, container) {

    // Manage arguments and assign defaults, 
    if (typeof container == 'undefined' ) container = document.body;
    if (null == (this.container = $(container))) throw("container is not valid");

    // Assign instance variables
    this.content = content;
    this.overlay = new Element('div', { 'class': 'd_overlay' }).hide();
    this.dialog = new Element('div', { 'class': 'd_dialog' }).hide();

    // Hide the overlay when clicked. Ignore clicks on the dialog.
    Event.observe(this.overlay, 'click', this.hide.bindAsEventListener(this));
    Event.observe(this.dialog, 'click',  function(event) { Event.stop(event) });
    
    // Insert the elements into the DOM
    this.dialog.insert(this.content);
    this.container.insert(this.overlay);
    this.container.insert(this.dialog);

    // Content may have been hidden if it is embedded in the page
    content.show();
    this.dialog.hide();
}

DialogOverlay.prototype.show = function() {
    new Effect.Appear(this.overlay, { duration: 0.5,  to: 0.8 });
    this.dialog.show();
    return this;
};
DialogOverlay.prototype.hide = function(event) {
    this.dialog.hide();
    this.overlay.hide();
    return this;
};