# System.Text

``` diff
 namespace System.Text {
     public class ASCIIEncoding : Encoding {
+        public override int GetByteCount(ReadOnlySpan<char> chars);
+        public override int GetBytes(ReadOnlySpan<char> chars, Span<byte> bytes);
+        public override int GetCharCount(ReadOnlySpan<byte> bytes);
+        public override int GetChars(ReadOnlySpan<byte> bytes, Span<char> chars);
     }
     public class UnicodeEncoding : Encoding {
+        public override ReadOnlySpan<byte> Preamble { get; }
     }
     public sealed class UTF32Encoding : Encoding {
+        public override ReadOnlySpan<byte> Preamble { get; }
     }
     public class UTF8Encoding : Encoding {
+        public override ReadOnlySpan<byte> Preamble { get; }
+        public override int GetByteCount(ReadOnlySpan<char> chars);
+        public override int GetBytes(ReadOnlySpan<char> chars, Span<byte> bytes);
+        public override int GetCharCount(ReadOnlySpan<byte> bytes);
+        public override int GetChars(ReadOnlySpan<byte> bytes, Span<char> chars);
     }
 }
```

