How does the C# compiler decide to emit retargetable assembly references?

Question

Retargetable assembly references have been introduced for the .NET Compact Framework and are now used to support Portable Class Libraries.

Basically, the compiler emits

Answer 1

For the assembly itself, it's an assembly flag, ie [assembly: AssemblyFlags(AssemblyNameFlags.Retargetable)].

Make note that this flag is meaningless outside of platform assemblies - custom assemblies cannot be retargetable.

For references, it's copied as part of the name from the assembly being referenced.