protected void checkIntNonNegative(CharSequence literal, int offset) throws DatatypeException {
        if (literal.length() == 0) {
            throw newDatatypeException("The empty string is not a valid non-negative integer.");
        }
        for (int i = 0; i < literal.length(); i++) {
            char c = literal.charAt(i);
            if (!isAsciiDigit(c)) {
                throw newDatatypeException(offset + i, "Expected a digit but saw ", c, " instead.");                            
            }
        }
    }
@param literal
@param offset TODO
@throws DatatypeException
src/nu/validator/datatype/AbstractInt.java