Image sprites are used in numerous web apps where multiple images are used. Rather than include each image as a separate image file, it is much more memory and bandwidth-friendly to send them as a single image, so the number of HTTP requests is reduced.
CSS gradients are new types of <image> added in the CSS3 Image Module. Using CSS gradients lets you display smooth transitions between two or more specified colors. This lets you avoid using images for these effects, thereby reducing download time and bandwidth usage. In addition, because the gradient is generated by the browser, objects with gradients look better when zoomed, and you can adjust your layout much more flexibly.
CSS counters are, in essence, variables maintained by CSS whose values may be incremented by CSS rules to track how many times they're used. This lets you adjust the appearance of content based on its placement in the document. CSS counters are an implementation of Automatic counters and numbering in CSS 2.1.
Usually HTML pages can be considered two-dimensional, because text, images and other elements are arranged on the page without overlapping. There is a single rendering flow, and all elements are aware of the space taken by others. The z-index attribute lets you adjust the order of the layering of objects when rendering content.
Stacking context is the three-dimensional conceptualization of HTML elements along an imaginary z-axis relative to the user who is assumed to be facing the viewport or the webpage. HTML elements occupy this space in priority order based on element attributes.
A media query consists of an optional media type and zero or more expressions that limit the style sheets' scope by using media features, such as width, height, and color. Media queries, added in CSS3, let the presentation of content be tailored to a specific range of output devices without having to change the content itself.
HTML Drag and Drop interfaces enable applications to use drag and drop features in Firefox and other browsers. For example, with these features, the user can select draggable elements with a mouse, drag the elements to a droppable element, and drop those elements by releasing the mouse button. A translucent representation of the draggable elements follows the mouse pointer during the drag operation.
IndexedDB is a low-level API for client-side storage of significant amounts of structured data, including files/blobs. This API uses indexes to enable high performance searches of this data. While DOM Storage is useful for storing smaller amounts of data, it is less useful for storing larger amounts of structured data. IndexedDB provides a solution. This is the main landing page for MDN's IndexedDB coverage — here we provide links to the full API reference and usage guides, browser support details, and some explanation of key concepts.
The Pointer Lock API (formerly called Mouse Lock API) provides input methods based on the movement of the mouse over time (i.e., deltas), not just the absolute position of the mouse cursor in the viewport. It gives you access to raw mouse movement, locks the target of mouse events to a single element, eliminates limits on how far mouse movement can go in a single direction, and removes the cursor from view. It is ideal for first person 3D games, for example.
The HTML5 specification brings several new elements to web developers allowing them to describe the structure of a web document with standard semantics. This document describes these elements and how to use them to define the desired outline for any document.
HTML5 provides an application caching mechanism that lets web-based applications run offline. Developers can use the Application Cache (AppCache) interface to specify resources that the browser should cache and make available to offline users. Applications that are cached load and work correctly even if users click the refresh button when they are offline.
The Media Capture and Streams API, often called the Media Stream API or the Stream API, is an API related to WebRTC which supports streams of audio or video data, the methods for working with them, the constraints associated with the type of data, the success and error callbacks when using the data asynchronously, and the events that are fired during the process.