Filed FB24392978 for this clarification to be added to the documentation.

Thank you for this clarification. It would be nice to have this clarified on the relevant structures. Is feedback assistant the right place for that?

Thank you for your response. I'm slightly confused though, if there is no null MTLResourceID then on what value would is_null_acceleration_structure (metal shading language 6.19.1) return true on? It would be nice to be able to disable instances without knowing a separate valid acceleration structure, if the mask is 0 then does the acceleration structure id have to be valid?