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DynamicBuffer_v2: Get a sequence of buffers that represents the underlying memory.
mutable_buffers_type data( std::size_t pos, std::size_t n);
Position of the first byte to represent in the buffer sequence
The number of bytes to return in the buffer sequence. If the underlying memory is shorter, the buffer sequence represents as many bytes as are available.
            An object of type mutable_buffers_type
            that satisfies MutableBufferSequence requirements, representing the basic_string
            memory.
          
            The returned object is invalidated by any dynamic_string_buffer
            or basic_string member
            function that resizes or erases the string.