The .NET Core is now OpenSource. It's on GitHub. For the more fanatics, Microsoft had already release "a working implementation of the ECMA CLI and the ECMA C# language specification" back in 2001 and 2006. It was the Shared Source Common Language Infrastructure (SSCLI), also known as Rotor. Now it's the official core. You can read the release info here: .NET Framework blog.
But, guess what: They are human at Microsoft. And they write like "normal" people. Take a look:
We're doomed! (Source: ConcurrentExclusiveSchedulerPair.cs)
Maintenance (Source: Parallel.cs)
Zombies... (Source: Scheduling.cs)
Curve ball (Source: DebugTypeDescriptor.cs)
Legacy (Source: isymwrappercore.cs)
I can't prove it! (Source: EventLogInternal.cs)
Don't touch (Source: compareinfo.cs)
I don't understand (Source: methodbuilder.cs)
Hooker? (Source: console.cs)
This was adapted from another blog. You can read part of the original article here (pt-BR).