void registerExtensionDef(ExtensionDef extensionDef) {
        Class<? extends IDomainExtension> extClazz = extensionDef.getExtClazz();
        if (extensionDefMap.containsKey(extClazz)) {
            throw BootstrapException.ofMessage("Pattern(code=", code, ") can hold ONLY one instance on ", extClazz.getCanonicalName(),
                    ", existing ", extensionDefMap.get(extClazz).toString(), ", illegal ", extensionDef.toString());