Z<> in =item

In perldiag.pod, there is a line like this

=item Z<>500 Server error

All the other items form a definition list.  My guess is that this is to 
make sure that the 500 isn't mistaken for a numbered =item in the list. 
  However, with html, anyway, I don't see any difference in the output 
with and without the Z<>, and podchecker ignores the Z<> and says that 
the list has mismatched item types.

Can someone explain?