  We present an explicit realization of the Chen et al. approach to the proton
spin decomposition in terms of Wilson lines, generalizing the light-front
gauge-invariant extensions discussed recently by Hatta. Particular attention is
drawn to the residual gauge freedom by further separating the pure-gauge term
into contour and residual terms. We show that the kinetic orbital angular
momentum operator can be expressed in terms of the Wigner operator only when
the momentum variable is integrated over. Finally, we confirm from twist-2
arguments that the advanced, retarded and antisymmetric light-front canonical
orbital angular momenta are the same.
