<PackageReference Include="System.Diagnostics.DiagnosticSource" Version="10.0.2" />

System.Text.ValueStringBuilder

namespace System.Text { internal ref struct ValueStringBuilder { public int Length { get; } public ValueStringBuilder(Span<char> initialBuffer); public ReadOnlySpan<char> AsSpan(int start, int length); public void Append(char c); public void Append(string s); public void Append(ReadOnlySpan<char> value); public void Dispose(); } }