In a coordinated announcement, three major browser vendors have agreed to consolidate their individual web API reference documentation into Mozilla's MDN and have formed an advisory group to guide future efforts.
The end result is intended to be a single source of truth that web developers can read and rely on to be kept up-to-date by those that actually build browsers. In a blog post from Microsoft, senior dev writer Erika Doyle Navara wrote that they have "started redirecting over 7,700 MSDN pages to corresponding topics in the MDN web docs library" and have made 5,000 edits on MDN to update the compatability tables for Edge.
A post from Google focused on the new Product Advisory Board and how it will make "MDN the best source of up-to-date, comprehensive documentation on the web and aligns closely with our goal to make it easier to build for the web as a whole." The current board includes members from Microsoft, Google, Mozilla, Samsung, and the W3C. Noticeably absent from this announcement and group is Apple.
Earlier this year, Mozilla announced the retooling of MDN and their goal of making it the "single best resource for Web docs". This new, consolidated announcement from the browser vendors is a major step in making that a reality.
In a typical day, a web developer may spend a significant amount of time scouring the web, searching for how a particular feature works in different browsers. Tools such as MDN, the Kangax Compatability Tables, and caniuse.com are bookmarked by many a web developer. These will continue to be valuable tools, but knowing that the browser vendors are actively updating the MDN documents provides a higher level of confidence.
Microsoft devs have long gone to MSDN for any Microsoft related developer documentation, so this represents a significant strategy shift for the company. To be clear, Microsoft has not shifted all of their Edge related docs en masse. The Edge developer documentation on MSDN still provides information on developing for Edge on Windows-specific topics. But, the current search experience is still a little fragmented. A recent Google search for Edge sessionStorage, Microsoft's own document describing the feature came up first; links to MDN were results 4-6.
MDN is a wiki, and developers can login with a GitHub account to make changes. Mozilla says that this year alone, "8,021 users made 76,203 edits".
In 2012, there was an attempt by the W3C to create the Web Platform Docs, with a similar goal. That project was discontinued in 2015. MDN has been around since 2005.