Clarification regarding the spatial grid stagger in base standard

[skuschel]

I was looking into the grid staggering and relalized that the temporal stagger is expressed in terms of a non-zero timeOffset as clearly stated here:
https://github.com/openPMD/openPMD-standard/blob/latest/STANDARD.md#required-attributes-for-the-basepath

For the spatial stagger this is not as clearly written. Assuming we have a field B/x which is offset by half a grid cell in a 1D simulation.

• The attibute postion will have to be 0.5.
• Will the value of positionOffset be set to 0.5*dx or not? I do not find a clear statement regarding this question. I believe it should, but I believe we should make it explicitly clear, that the information of a spatial stagger is saved in two distinct places. Or am I missing something?

Let me know if you concur and I will create a PR.

Related to SmileiPIC/Smilei#682