'member': non CLS-compliant members cannot be abstract
A class member cannot be both abstract and non-compliant with the Common Language Subset (CLS). The CLS specifies that all class members shall be implemented.
The following sample generates CS3011:
using System; [assembly:CLSCompliant(true)] public abstract class I { [CLSCompliant(false)] public abstract int mf(); // CS3011 // OK [CLSCompliant(false)] public void mf2() { } } public class C : I { public override int mf() { return 1; } public static void Main() { } }