  The discussion regarding the numerical integration of the polarized radiative
transfer equation is still open and the comparison between the different
numerical schemes proposed by different authors in the past is not fully clear.
Aiming at facilitating the comprehension of the advantages and drawbacks of the
different formal solvers, this work presents a reference paradigm for their
characterization based on the concepts of order of accuracy, stability, and
computational cost. Special attention is paid to understand the numerical
methods belonging to the Diagonal Element Lambda Operator family, in an attempt
to highlight their specificities.
