  Exploring the similarities between the Chen \emph{et al.} approach, where
physical and gauge degrees of freedom of the gauge potential are explicitly
separated, and the background field method, we provide an alternative point of
view to the proton spin decomposition issue. We show in particular that the
gauge symmetry can be realized in two different ways, and discuss the relations
between the concepts of path dependence, Stueckelberg dependence and background
dependence. Finally, we argue that path/Stueckelberg/background-dependent
decompositions of the proton spin are in principle measurable and therefore
physically meaningful.
