What's the difference between -seed and -svseed in irun?

There are two options to control random seed when using irun: -seed, -svseed.

It seems that these two options is doing the same thing: set a random seed to RNG. And I tried many times, I can't find difference between these two options. Both can be used to control Verilog/SystemVerilog randomization, for example:

-seed 123

-svseed 123

-seed random

-svseed random

So, what's the difference between these two options?

Thanks!