docs: public boolean isExcludeUnlistedClasses()
      {
          // The JAXB generated classes will return 'false' if the stanza was
          // specified, but without a value
          Boolean exclude = ivPUnit.isExcludeUnlistedClasses();
  
          // The version 1.0 persistence.xsd spelled out the default for
          // exclude-unlisted-classes is false.
          //
          // This means there are 4 choices:
          //   <exclude-unlisted-classes> not specified                   --> Not excluded
          //   <exclude-unlisted-classes>false</exclude-unlisted-classes> --> Not excluded
          //   <exclude-unlisted-classes>true</exclude-unlisted-classes>  --> Excluded
          //   <exclude-unlisted-classes/>                                --> Not excluded
          //
          // The last choice contradicts the sample's implied semantics.
          // Patrick Linskey confirms that this is a problem in the JPA spec and
          // the spec decided that the XSD is the final correct specification.
          // i.e. unlisted classes are excluded iff
          // <exclude-unlisted-classes>true</exclude-unlisted-classes> is used.
  
          if (JPA_OVERRIDE_EXCLUDE_UNLISTED_CLASSES)
          {
              // If "com.ibm.jpa.override.exclude.unlisted.classes" system property is set to
              // true, all variations of <exclude-unlisted-classes> specification in
              // persistence unit are treated as
              // <exclude-unlisted-classes>true</exclude-listed-classes>, which matches the
              // original intent as used in the JPA spec samples.
              //
              // This is NOT the default behavior.
              if (exclude != null)
              {
                  exclude = Boolean.TRUE;
  
                  if (TraceComponent.isAnyTracingEnabled() && tc.isDebugEnabled())
                      Tr.debug(tc, "isExcludeUnlistedClasses : overriden to TRUE");
              }
          }
  
          // The default when not present at all is 'false'
          if (exclude == null)
          {
              exclude = Boolean.FALSE;
  
              if (TraceComponent.isAnyTracingEnabled() && tc.isDebugEnabled())
                  Tr.debug(tc, "isExcludeUnlistedClasses : defaulted to FALSE");
          }
  
          return exclude.booleanValue();
      }