Search by learning step

I think it would be useful to be able to search for unlapsed learning cards by learning step.
For example, if my learning steps are 1d, 3d, 5d, then searching for (prop:ivl=3 is:learn -is:review) should show me all the unlapsed learning cards on the second step, but this doesn’t happen. It seems the prop:ivl filter only looks at cards that have graduated at least once