RequestParameterVersion version = RequestParameter.versionParameter(_request.parameters().get(RequestParameter.ParameterVersion));
if (version.versionAll()) {
iterator = new FullContentIterator(_content);
} else if (version.versionChangesSince()) {
iterator = new ChangesSinceContentIterator(_content, ((RequestParameterVersionChanges)version).versionNumber());
} else if (version.versionCurrent()) {
iterator = new CurrentContentIterator(_content);
} else if (version.versionSingle()) {
iterator = new VersionContentIterator(_content, ((RequestParameterVersionSingle)version).versionNumber());
}