  I review the resummation formalism for organizing large logarithms in
perturbative expansion of collinear subprocesses through the variation of
Wilson lines off the light cone. A master equation is derived, which involves
the evolution kernel resulting from this variation. It is then demonstrated
that all the known single- and double-logarithm summations for a parton
distribution function or a transverse-momentum-dependentparton distribution can
be reproduced from the master equation by applying appropriate soft-gluon
approximations to the evolution kernel. Moreover, jet substructures,
information which is crucial for particle identification at the Large Hadron
Collider and usually acquired from event generators, can also be calculated in
this formalism.
