  We consider the problems of gauge invariance, path-dependence and treatment
of overlapping UV/rapidity divergences peculiar to the transverse-momentum
dependent parton distribution functions (TMDs). For different formulations of
the TMDs available in the literature, we check the consistency of the TMD
matrix elements with the collinear parton distribution functions possessing the
well-known operator structure. Comparative on- and off-light-cone layout of the
Wilson lines which secure the gauge-invariance of the TMDs is presented and
briefly discussed.
