@Override
    public void validateXMLFor(Optional<Version> vespaVersion) throws IOException {
        Version modelVersion = vespaVersion.orElse(Vtag.currentVersion);
        ApplicationPackageXmlFilesValidator validator = ApplicationPackageXmlFilesValidator.create(appDir, modelVersion);
        validator.checkApplication();
        validator.checkIncludedDirs(this);
    }
Reads a ranking expression from file to a string and returns it.

@param name the name of the file to return,
            relative to the search definition directory in the application package
@return the content of a ranking expression file
@throws IllegalArgumentException if the file was not found or could not be read
config-application-package/src/main/java/com/yahoo/config/model/application/provider/FilesApplicationPackage.java