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copied!<p>Well break it down into pieces. What is a Web browser? What does it do? It:</p> <ul> <li><strong>Fetches external content.</strong> So you need a HTTP library or (not recommended) write this yourself. There's a lot of complexity/subtlety to the HTTP protocol eg handling of expires headers, different versions (although it's mostly 1.1 these days), etc;</li> <li><strong>Handles different content types.</strong> Theres a Windos registry for this kind of thing that you can piggyback. I'm talking interpreting content based on MIME type here;</li> <li><strong>Parses HTML and XML</strong>: to create a DOM (Document Object Model);</li> <li><strong>Parses and applies CSS</strong>: this entails understanding all the properties, all the units of measure and all the ways values can be specified (eg "border: 1px solid black" vs the separate border-width, etc properties);</li> <li><strong>Implements the W3C visual model</strong> (and this is the real kicker); and</li> <li><strong>Has a Javascript engine</strong>.</li> </ul> <p>And that's basically a Web browser in a nutshell. Now some of these tasks are incredibly complex. Even the easy sounding ones can be hard. Take fetching external content. You need to deal with use cases like:</p> <ul> <li>How many concurrent connections to use?</li> <li>Error reporting to the user;</li> <li>Proxies;</li> <li>User options;</li> <li>etc.</li> </ul> <p>The reason I and others are colletively raising our eyebrows is the rendering engine is hard (and, as someone noted, man years have gone into their development). The major rendering engines around are:</p> <ul> <li><strong>Trident:</strong> developed by Microsoft for Internet Explorer;</li> <li><strong>Gecko:</strong> used in Firefox;</li> <li><strong>Webkit:</strong> used in Safari and Chrome 0-27;</li> <li><strong>KHTML:</strong> used in the KDE desktop environment. Webkit forked from KHTML some years ago;</li> <li><strong>Elektra:</strong> used in Opera 4-6;</li> <li><strong>Presto:</strong> used in Opera 7-12;</li> <li><strong>Blink:</strong> used in Chrome 28+, Opera 15+, webkit fork;</li> </ul> <p>The top three have to be considered the major rendering engines used today.</p> <p>Javascript engines are also hard. There are several of these that tend to be tied to the particular rendering engine:</p> <ul> <li><strong>SpiderMonkey:</strong> used in Gecko/Firefox;</li> <li><strong>TraceMonkey:</strong> will replace SpiderMonkey in Firefox 3.1 and introduces JIT (just-in-time) compilation;</li> <li><strong>KJS:</strong> used by Konqueror, tied to KHTML;</li> <li><strong>JScript:</strong> the Javascript engine of Trident, used in Internet Explorer;</li> <li><strong>JavascriptCore:</strong> used in Webkit by the Safari browser;</li> <li><strong>SquirrelFish:</strong> will be used in Webkit and adds JIT like TraceMonkey;</li> <li><strong>V8:</strong> Google's Javascript engine used in Chrome and Opera;</li> <li>Opera (12.X and less) also used its own.</li> </ul> <p>And of course there's all the user interface stuff: navigation between pages, page history, clearing temporary files, typing in a URL, autocompleting URLs and so on.</p> <p>That is a <strong>lot</strong> of work.</p>

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