forgot to clarify that in this example wiggle will vary the incoming property value by 50, so if this is opacity for example and it is set to 50, then wiggle will output values from 0 to 100.
I am just pointing this out because it can be a bit confusing since the output is then defined by the expression, in this case 0 or 100, not the values output by the wiggle (although in this case i set it up so it would essentially be the same). But you could for example set opacity to 1 and then wiggle that by 1 and set the expression as follows:
if(v < 1)v=0;
if(v > 1)v=100;
and still get the same output of 0 or 100.