Testing momentum dependence of the nonperturbative hadron structure in a global QCD analysis

We discuss strategies for comparisons of nonperturbative QCD predictions parton distribution functions (PDFs) with high-energy experiments in the region large partonic momentum fractions $x$. Analytic functional forms PDFs cannot be uniquely determined solely based on discrete experimental measurements because a mathematical property mimicry PDF parametrizations that we prove using representation B\'ezier curves. Predictions approaches $x$ dependence instead should cast form enables decisive against measurements. effective power laws $(1-x)$ may play this role. Expectations proton quark counting rules are compared satisfied by CT18 next-to-next-to-leading order distributions. comment implications studies pion, particular comparison phenomenological PDFs.