Kxxxxxxx Lyyyyyyy Lzzzzzzz value
Coupled mutual inductance.
K couples two inductors. The value is the coefficient of coupling. Using the dot convention, place a dot on the first node of each inductor.
The coefficient of coupling is given by K = m[i][j] / sqrt(L[i] L[j]). K is always positive and less than 1.
This version of mutual inductance is only supported in Spice syntax, because the connections are inductors. If you are using any other syntax, you can make a Spice subcircuit containing the entire transformer.