I need to clarify a little bit more, because I don't believe I did adequately.

In JPA 1.0, <exclude-unlisted-classes> had the following usage:

1. Omitted means don't exclude / do scan.
2. <exclude-unlisted-classes /> means exclude / don't scan.
3. <exclude-unlisted-classes>false</exclude-unlisted-classes> means don't exclude / do scan.
4. <exclude-unlisted-classes>true</exclude-unlisted-classes> means exclude / don't scan.

As of JPA 2.0, <exclude-unlisted-classes> has the following usage:

1. Omitted means exclude / don't scan.
2. <exclude-unlisted-classes /> means exclude / don't scan.
3. <exclude-unlisted-classes>false</exclude-unlisted-classes> means don't exclude / do scan.
4. <exclude-unlisted-classes>true</exclude-unlisted-classes> means exclude / don't scan.

With this clarification, my suggested code needs to be tweaked slightly:

private void bindPersistenceUnit(ParsedPersistenceXmlDescriptor persistenceUnit, Element persistenceUnitElement) {
        ...
        persistenceUnit.setExcludeUnlistedClasses( !isJpaGte20 );
        NodeList children = persistenceUnitElement.getChildNodes();
        for ( int i = 0; i < children.getLength() ; i++ ) {
            ...
                else if ( tag.equals( "exclude-unlisted-classes" ) ) {
                    persistenceUnit.setExcludeUnlistedClasses( extractBooleanContent(element, true) );
                }
            ...
        }
    }
    ...
    private static boolean extractBooleanContent(Element element, boolean defaultBool) {
        String content = extractContent( element, null );
        if (content != null && content.length() > 0) {
            return Boolean.valueOf(content);
        }
        return defaultBool;
    }