in src/main/java/org/apache/maven/resolver/internal/ant/types/RemoteRepository.java [195:202]
protected static void checkUpdates(String updates) {
if (!RepositoryPolicy.UPDATE_POLICY_ALWAYS.equals(updates)
&& !RepositoryPolicy.UPDATE_POLICY_DAILY.equals(updates)
&& !RepositoryPolicy.UPDATE_POLICY_NEVER.equals(updates)
&& !updates.startsWith(RepositoryPolicy.UPDATE_POLICY_INTERVAL)) {
throw new BuildException("'" + updates + "' is not a permitted update policy");
}
}