http://arstechnica.com/information-technology/2016/05/microsoft-unveils-new-effort-to-make-its-developer-it-documentation-great-again/:

Some teams within Microsoft, such as those developing ASP.NET and .NET Core, had already open sourced their documentation. On the new site, all documentation will be handled similarly. Every article will have an "edit" button enabling changes and fixes to be proposed. These changes will be handled as pull requests on GitHub, with the documentation itself using the popular Markdown markup language.

Just one problem: while Microsoft itself uses the term “open sourced” https://docs.microsoft.com/teamblog/introducing-docs-microsoft-com/:

All documentation on docs.microsoft.com is open sourced and designed to allow community contributions.

Nowhere does it actually spell out what the copyright licence is. Clicking on the “Terms of Use” link takes you here https://www.microsoft.com/en-us/legal/intellectualproperty/copyright/default.aspx, where it says

Personal and Non-Commercial Use Limitation

Unless otherwise specified, the Services are for your personal and non-commercial use. You may not modify, copy, distribute, transmit, display, perform, reproduce, publish, license, create derivative works from, transfer, or sell any information, software, products or services obtained from the Services.