Perhaps because you're being pedantic about .NET versus the CLI? The CLI spec is...

MichaelGG on Nov 2, 2013 | parent | context | favorite | on: An analysis of the C#/.NET platform

Perhaps because you're being pedantic about .NET versus the CLI? The CLI spec is a standard and open source. Microsoft's own version isn't open source (well, they did release an "open" source version, Rotor). But Mono's is.