Avgrund is a jQuery plugin for modal boxes and popups. It uses interesting concept showing depth between popup and page. It works in all modern browsers and gracefully degrade in those that do not support CSS transitions and transformations (e.g. in IE 6-9 has standard behavior). File size is under 2Kb, MIT Licensed.
In user interface design, a modal window is a graphical control element subordinate to an application's main window which creates a mode where the main window can't be used. The modal window is a child window that requires users to interact with it before it can return to operating the parent application, thus preventing the workflow on the application main window. Modal windows are often called heavy windows or modal dialogs because the window is often used to display a dialog box.
User interfaces use modal windows to prompt users to act before they can complete their task. When they’re used right, they can ease the user’s task. When they’re used wrong, they can get in the way of the user’s task. Here are some best practices that will help you to design user-friendly modal windows.
A modal window is a secondary window that opens on top of the main one. Users have to interact with it before they can carry out their task and return to the main window. You should use modal windows when there are steps the user needs to do before the task can be completed. Using a modal window instead of a full page allows users to maintain the context of their task.