The following method does not allow syslog tags to include characters other than alphanumeric characters, for example, underscores are not allowed. The syslog spec allows 

public void setTag(final String tag) {
    .
    .
    .
            if (NOT_ALPHANUM.matcher(newTag).find()) {
                throw new IllegalArgumentException("tag contains non-alphanumeric characters");
            }
    .
    .
    .
}