Hello,
I would like to propose add mask layer to FFT spectrum viewer.
Will be useful for EMC modelling for CISPR22/32, CISPR25, MIL-STD-461G for example. Mask can be defined as PWL in external file.
This looks like plot from LTpowerCAD.
I think adding graphic layer over any waveform plots will be very nice feature.
Eye mask for differential pairs with .tran analysis, for example.