  Reporting about the Wigner formalism for describing Dirac spinor structures
through a covariant phase-space formulation, the quantum information
quantifiers for purity and mutual information involving spin-parity (discrete)
and position-momentum (continuous) degrees of freedom are consistently
obtained. For Dirac spinor Wigner operators decomposed into Poincar\'e classes
of $SU(2) \otimes SU(2)$ spinor couplings, a definitive expression for quantum
purity is identified in a twofold way: firstly, in terms of phase-space
positively defined quantities, and secondly, in terms of the {\em spin-parity
traced-out} associated density matrix in the position coordinate
representation, both derived from the original Lorentz covariant phase-space
Wigner representation. Naturally, such a structure supports the computation of
relative (linear) entropies respectively associated to discrete (spin-parity)
and continuous (position-momentum) degrees of freedom. The obtained theoretical
tools are used for quantifying (relative) purities, mutual information as well
as, by means of the quantum concurrence quantifier, the spin-parity quantum
entanglement, for a charged fermion trapped by a uniform magnetic field which,
by the way, has the phase-space structure completely described in terms of
Laguerre polynomials associated to the quantized Landau levels. Our results can
be read as the first step in the systematic computation of the elementary
information content of Dirac-like systems exhibiting some kind of confining
behavior.
