[doc] clarify Std.downcast() wrt interfaces

std/Std.hx

@@ -34,17 +34,17 @@ extern class Std {
 	public static function is( v : Dynamic, t : Dynamic ) : Bool;
 
 	/**
-		Checks if object `value` is an instance of class `c`.
+		Checks if object `value` is an instance of class or interface `c`.
 
-		Compiles only if the class specified by `c` can be assigned to the type
+		Compiles only if the type specified by `c` can be assigned to the type
 		of `value`.
 
 		This method checks if a downcast is possible. That is, if the runtime
-		type of `value` is assignable to the class specified by `c`, `value` is
+		type of `value` is assignable to the type specified by `c`, `value` is
 		returned. Otherwise null is returned.
 
-		This method is not guaranteed to work with interfaces or core types such
-		as `String`, `Array` and `Date`.
+		This method is not guaranteed to work with core types such as `String`,
+		`Array` and `Date`.
 
 		If `value` is null, the result is null. If `c` is null, the result is
 		unspecified.