There is an example of stepping sets of parameters. In this case the parameter
voltage(Vds) and a set of prameter pairs(W,L) are stepped in a nested loop. 
This requires to use the table()-function for W and for L.

Files > Examples > Educational >MOSFET parameter sweep > MOS_gm_gmb_gds_ro.asc


This example also shows the advanced usage of plot functions.