Articles agree in gender to the noun they specify. The values
masculine and feminine and common are pertinent to the
class. Note that
this last value does not apply in presence of the value indf (see
below).
The value common can be seen as a multilabel whose semantics
is a ``disjunction" operation:
in fact, the value c is a macro for m 
f.
It is used, when tagging,
for the graphical form l' elision of lo and
la when the context is not sufficient to solve the underspecification,
i.e. when the gender of the agreed noun is undecided:
l'insegnante.