public static boolean isValidNmtoken(String nmtoken) {
        if (nmtoken.length() == 0) {
            return false;
        }
        for (int i = 0; i < nmtoken.length(); i++) {
            char ch = nmtoken.charAt(i);
            if (!isName(ch)) {
                return false;
            }
        }
        return true;
    }
Check to see if a string is a valid Nmtoken according to [7]
in the XML 1.0 Recommendation

@param nmtoken string to check
@return true if nmtoken is a valid Nmtoken
stroom-util/src/main/java/stroom/util/xml/XMLChar.java