# System.Text

``` diff
 namespace System.Text {
     public sealed class StringBuilder : ISerializable {
+        public StringBuilder AppendFormat(IFormatProvider? provider, string format, ReadOnlySpan<object?> args);
+        public StringBuilder AppendFormat(string format, ReadOnlySpan<object?> args);
+        public StringBuilder AppendJoin(char separator, ReadOnlySpan<object?> values);
+        public StringBuilder AppendJoin(char separator, ReadOnlySpan<string?> values);
+        public StringBuilder AppendJoin(string? separator, ReadOnlySpan<object?> values);
+        public StringBuilder AppendJoin(string? separator, ReadOnlySpan<string?> values);
     }
 }
```

