The Birth of Microsoft’s New Web Rendering Engine
As we announced last month, Project Spartan will be the new browser across all Windows 10 devices, from phones to tablets, PCs and beyond.
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First, the Web is built on the principle of multiple independent, yet interoperable implementations of Web standards and we felt it was important to counter movement towards a monoculture on the Web. Second, given the engineering effort required, we found that we could deliver an interoperability focused engine to customers significantly faster if we started from our own engine (especially if unshackled from legacy compatibility concerns), rather than building up a new browser around an open-source engine.
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As detailed in Jacob Rossi’s article for Smashing Magazine, the new engine began as a fork of MSHTML.dll but has since diverged very quickly. By making this split, we were able to keep the major subsystem investments made over the last several years, while allowing us to remove document modes and other legacy IE behaviors from the new engine. On the other hand, our legacy engine (MSHTML.dll) can remain largely unchanged (outside of security and other high priority fixes) to help guarantee legacy compatibility for our enterprise customers. We also built up capabilities to switch between the legacy and new rendering engines seamlessly.
A clean break also necessitates a new user-agent string to ensure that no IE-specific code was being sent. This built upon a long browser history of using whatever tokens are necessary to get the desired content from servers. Although this meant a lower compatibility rate initially, it was also useful to reveal interoperability issues that needed to be fixed!
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However, a new engine was not enough – we also needed to significantly revamp how we find, track and fix issues on the long tail of the Web. To do so, we do daily analysis on trillions of URLs crawled in conjunction with Bing to detect patterns that exist in the head of the Web and the tail of the Web. By fixing these patterns, sites just end up working. This data is augmented by thousands of daily feedback reports from users via the “smiley face” icon.
