struct Utf8ValueStringBuilder
{
  void Append(char value, int repeatCount);
  void Append(ReadOnlySpan<char> value);
  void AppendLine(ReadOnlySpan<char> value);
  void Clear();
}
struct Utf16ValueStringBuilder
{
  void Append(char value, int repeatCount);
  void AppendLine(ReadOnlySpan<char> value);
  void Clear();
  void Replace(char oldChar, char newChar);
  void Replace(char oldChar, char newChar, int startIndex, int count);
  void Replace(string oldValue, string newValue);
  void Replace(ReadOnlySpan<char> oldValue, ReadOnlySpan<char> newValue);
  void Replace(string oldValue, string newValue, int startIndex, int count);
  void Replace(ReadOnlySpan<char> oldValue, ReadOnlySpan<char> newValue, int startIndex, int count);
  void Remove(int startIndex, int length);
  void Insert(int index, string value, int count);
  void Insert(int index, string value);
  void Insert(int index, ReadOnlySpan<char> value, int count);
}