code: func (b *Buffer) WriteByte(c byte) error {
  	m := b.grow(1)
  	b.buf[m] = c
  	return nil
  }
docs: // WriteByte appends the byte c to the buffer, growing the buffer as needed.
  // The returned error is always nil, but is included to match bufio.Writer's
  // WriteByte. If the buffer becomes too large, WriteByte will panic with
  // bytes.ErrTooLarge.