When should data_offset in multi array layout not be zero

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Multiarray layout messages contain a data_offset field (in multi_array_layout__struct.h of std_msgs). I have implemented support for multiarrays in the Ada client library and I honor that field when interpreting a received message, but when creating a new one I always set that field to zero (and it seemingly works).

I guess the field is there for alignment issues, but I'd like to know for sure how it is expected to be used. The only documentation I've found is in MultiArrayLayout.msg where it says that those are front padding bytes, but it doesn't go into further details about when such padding is needed. Thanks for any clarification.