dirhandle, usually the real dirhandle name. If DIRHANDLE is an undefined
scalar variable (or array or hash element), the variable is assigned a
reference to a new anonymous dirhandle; that is, it's autovivified.
-DIRHANDLEs have their own namespace separate from FILEHANDLEs.
+Dirhandles are the same objects as filehandles; an I/O object can only
+be open as one of these handle types at once.
See the example at L<C<readdir>|/readdir DIRHANDLE>.