Mass formulae for light meson multiplets derived by means of exotic
commutator technique are written for complex masses and considered as complex
mass sum rules (CMSR). The real parts of the (CMSR) give the well known mass
formulae for real masses (Gell-Mann--Okubo, Schwinger and Ideal Mixing ones)
and the imaginary parts of CMSR give appropriate sum rules for the total
hadronic widths - width sum rules (WSR). Most of the observed meson nonets
satisfy the Schwinger mass formula (S nonets). The CMSR predict for S nonet
that the points (m,Γ) form the rectilinear stitch (RS) on the complex
mass plane. For low-mass nonets WSR are strongly violated due to
``kinematical'' suppression of the particle decays, but the violation decreases
as the mass icreases and disappears above ∼1.5GeV. The slope ks of
the RS is not predicted, but the data show that it is negative for all S nonets
and its numerical values are concentrated in the vicinity of the value -0.5. If
ks is known for a nonet, we can evaluate ``kinematical'' suppressions of its
individual particles. The masses and the widths of the S nonet mesons submit to
some rules of ordering which matter in understanding the properties of the
nonet. We give the table of the S nonets indicating masses, widths, mass and
width orderings. We show also mass-width diagrams for them. We suggest to
recognize a few multiplets as degenerate octets. In Appendix we analyze the
nonets of 1+ mesons.Comment: 20 pages, 3 figures; title and discussion expanded; additional text;
final version accepted for publication in EPJ