  Including the effects of the ${\cal{O}}(\gtrsim 1 {\rm GeV})$ masses of the
charm quark, $\tau$ lepton and target nucleon in DIS phenomenology is discussed
with applications to CC neutrino DIS: Neutrino data for $F_2$ are revisited
within the global analysis framework. A fully differential calculation refines
the CC charm production process as a gate to extract $\{s(x), {\bar s} (x) \}$.
New results are presented for a "heavy quark" version of the CTEQ6 set of PDFs
and for ($\nu_{\mu} \to \nu_{\tau}$ oscillation-signal) $\tau$ neutrino cross
sections.
