I'm not sure what is meant by this sentence.
Motion is defined in relativity by observer's point of view.
To put this into its a priori form - any measurement and experiment will have the values which are associated with its assumed observer. I'm not sure how you got this out of what I said. I don't even know what you mean, here. The geometry of space is determined a priori by the existence of an observer and that observer's motion relative to other observables in space. I guess what I'm not sure about here is what you mean by material content.