private String servicesFileName() {
        String servicesFile = FilesApplicationPackage.SERVICES;
        if ( ! appDirs.file(servicesFile).exists()) {
            throw new IllegalArgumentException("Application package in " + appDirs.root() +
                                               " must contain " + FilesApplicationPackage.SERVICES);
        }
        return servicesFile;
    }
Validation of xml files in application package against RELAX NG schemas.

@author hmusum
config-application-package/src/main/java/com/yahoo/config/model/application/provider/ApplicationPackageXmlFilesValidator.java