+Log sub calls and exits via the L<enter_sub>/L<leave_sub> functions,
+but only if they're called with a log level that is falsish
+(e.g. none, C<undef>, 0).
+
+=item C<TRACE2>
+
+Log sub calls and exits via the L<enter_sub>/L<leave_sub> functions
+even if they're called with a log level of 2. Will only have an effect
+if C<TRACE> is set as well.