  In the two papers published recently, we apply collinear expansion to both
inclusive ($e^+ e^- \to h+X$) and semi-inclusive ($e^+ e^- \to h + \bar q + X$)
hadron production in $e^+ e^-$ annihilation to derive a formalism suitable for
a systematic study of leading as well as higher twist contributions to
fragmentation functions at the tree level. We carry out the calculations for
hadrons with spin-0, spin-1/2 as well as spin-1. This proceeding is mainly a
summary of these two papers.
