  It is commonly assumed that the most correct description of the
electromagnetic world is the abstract one, and that topological constructs such
as lines of force are not covariant. In the present paper, we show that for a
$y$-invariant system with a $p$-polarized electromagnetic field, it is possible
to construct absolute (i.e. Lorentz invariant) lines, which we call electric
spaghettis (ESs). The electromagnetic field is fully described by the ES
topology that transcend the limit between space and time, plus a new invariant,
the characteristic parameter $\eta$. In a Fabry-Perot resonant slit-grating,
three ES patterns can be distinguished, corresponding to three regions: null
straight lines in plane wave regions, rounded rhombuses in the interference
region inside the grating, and Bernoulli's logarithmic spiral patterns - the
first ever described fractals - in the funneling region.
