This was set to the `nidm` namespace when we had a slightly different perspective on the terms. The idea was to put in software-specific namespaces the terms that would have different definition across software. While SPM does not have a centre of gravity, the idea was that if it would then the definition would most probably be the same as the FSL one, hence the `nidm` namespace. Given our new perspective (everything that is not common across software is in a software-specific namespace) I agree with you.