Dialogs and overlays present content that appears to float over the page. Dialogs usually offer richer interactive content like embedded form elements, buttons, and links, and require a decision or input from the user; overlays typically present read-only content. The wide range of uses for dialogs and overlays include:
• Presenting system error messages and confirmations that require user interaction to dismiss
• Collecting user input in a form or multi-step wizard
• Displaying large version of a photo in a “lightbox” when a thumbnail image is clicked on the page
• Creating floating palettes and UI inspector windows in a web application, like a document editor
• Opening a “sticky” tooltip or mini-overlay ...