  Taking the tri-bimaximal flavor mixing pattern as a particular basis, we
propose a new way to expand the $3\times 3$ unitary
Pontecorvo-Maki-Nakagawa-Sakata (PMNS) lepton flavor mixing matrix $U$ in
powers of the magnitude of its smallest element $\xi \equiv \left|U^{}_{e
3}\right| \simeq 0.149$. Such a Wolfenstein-like parametrization of $U$ allows
us to easily describe the salient features and fine structures of flavor mixing
and CP violation, both in vacuum and in matter.
