purpose of HANDLER_BUFFER *buffer in read_multi_range_first

[Zardosht Kasheff]

Hello all,

In 5.1, what is the purpose of the parameter HANDLER_BUFFER *buffer in
the function handler::read_multi_range_first? I see that NDB uses it,
but I do not understand for what.

The comment just states:
 @param buffer              A HANDLER_BUFFER for internal handler usage.

Thanks
-Zardosht