A browser engine (also known as a layout engine or rendering engine) is a core software component of every major web browser. The primary job of a browser engine is to transform HTML documents and other resources of a web page into an interactive visual representation on a user's device.
Name and scopeEdit
A browser engine is not a stand-alone computer program but a critical piece of a larger program, such as a web browser, from which the term is derived. (The word "engine" is an analogy to the engine of a car.)
Besides "browser engine", two other terms are in common use regarding related concepts: "layout engine" and "rendering engine". In theory, layout and rendering (or "painting") could be handled by separate engines. In practice, however, they are tightly coupled and rarely considered separately.
In addition to layout and rendering, a browser engine enforces the security policy between documents, handles navigation through hyperlinks and data submitted through forms, and implements the Document Object Model (DOM) data structure exposed to page scripts.
Browser engines are used in other types of programs besides web browsers. Email clients need them to display HTML email. The Electron framework, which is powered by the two engines of the Google Chrome browser, has been used to create many applications.
Layout and renderingEdit
The layout of a web page is typically specified by Cascading Style Sheets (CSS). Each style sheet is a series of rules which the browser engine interprets. For example, some rules specify typography details, such as font, color, and text size. The engine combines all relevant CSS rules to calculate precise graphical coordinates for the visual representation it will paint on the screen.
Some engines may begin rendering before all of a page's resources are downloaded. This can result in visual changes as more data is received, such as images being gradually filled in or a flash of unstyled content.
Google originally used WebKit for its Chrome browser but eventually forked it to create the Blink engine. All Chromium-based browsers use Blink, as do applications built with CEF, Electron, or any other framework that embeds Chromium.
Although Apple permits third-party browsers as alternatives to Safari on iOS devices, all browsers distributed through its App Store must use WebKit as their engine. For example, Opera Mini for iOS uses WebKit, whereas all other Opera variants use Blink. (Opera formerly used its own proprietary Presto engine.)
Microsoft maintains its own proprietary EdgeHTML engine, which is the successor of its Trident engine. However, EdgeHTML is now only used for Universal Windows Platform apps, as the Edge browser has been remade with the Blink engine.
- "Behind the scenes of modern web browsers". Tali Garsiel. Retrieved 2018-04-21.
- "Gecko". Mozilla. Retrieved 2018-04-21.
- "Introducing Goanna". M.C. Straver. 2015-06-22. Retrieved 2018-04-21.
- Wikimedia Traffic Analysis Report - Browsers e.a.: Monthly requests or daily averages, for period: 1 Feb 2014 - 28 Feb 2014, Wikimedia
- Paul Festa (2003-01-14). "Apple snub stings Mozilla". CNET Networks. Archived from the original on 2012-10-25. Retrieved 2017-02-16.
- Bright, Peter (April 3, 2013). "Google going its own way, forking WebKit rendering engine". Ars Technica. Conde Nast. Retrieved March 9, 2017.
- Mackie, Kurt (10 December 2018). "Microsoft Edge Browser To Get New Rendering Engine but EdgeHTML Continues". Redmond Mag. Retrieved 21 December 2019.
- Belfiore, Joe (2018-12-06), Microsoft Edge: Making the web better through more open source collaboration, Microsoft