They show the DFA for it on the site, it's 3 states. There's a starting state for the first . and then two states that transition back and forth between whether z was the last character or not.
I think what's actually happening here is that they're doing the intersection on the DFAs and then producing a regex from the resulting DFA. The construction of a regex from a DFA is where things get ugly and weird.
I think what's actually happening here is that they're doing the intersection on the DFAs and then producing a regex from the resulting DFA. The construction of a regex from a DFA is where things get ugly and weird.