Support static abstract members in interfaces

Author: RexJaeschke

standard/patterns.md

@@ -447,9 +447,9 @@ relational_pattern
 
 Relational patterns support the relational operators `<`, `<=`, `>`, and `>=` on all of the built-in types that support such binary relational operators with both operands having the same type: `sbyte`, `byte`, `short`, `ushort`, `int`, `uint`, `long`, `ulong`, `char`, `float`, `double`, `decimal`, `nint`, `nuint`, and enums.
 
-It is a compile-time error if `constant_expression`is `double.NaN`, `float.NaN`, or `null_literal`.
+It is a compile-time error if *constant_expression*is `double.NaN`, `float.NaN`, or `null_literal`.
 
-When the input value has a type for which a suitable built-in binary relational operator is defined, the evaluation of that operator is taken as the meaning of the relational pattern.  Otherwise, the input value is converted to the type of `constant_expression` using an explicit nullable or unboxing conversion.  It is a compile-time error if no such conversion exists.  The pattern is considered to not match if the conversion fails.  If the conversion succeeds, the result of the pattern-matching operation is the result of evaluating the expression `e «op» v` where `e` is the converted input, «op» is the relational operator, and `v` is the `constant_expression`.
+When the input value has a type for which a suitable built-in binary relational operator is defined, the evaluation of that operator is taken as the meaning of the relational pattern.  Otherwise, the input value is converted to the type of *constant_expression* using an explicit nullable or unboxing conversion.  It is a compile-time error if no such conversion exists. It is a compile-time error if the input type is a type parameter constrained to, or a type inheriting, from `System.Numerics.INumberBase<T>` and the input type has no suitable built-in binary relational operator defined.  The pattern is considered to not match if the conversion fails.  If the conversion succeeds, the result of the pattern-matching operation is the result of evaluating the expression `e «op» v` where `e` is the converted input, «op» is the relational operator, and `v` is the *constant_expression*.
 
 > *Example*:
 >