private static double getDoubleAttribute(Attributes atts, String name) {
        String str = atts.getValue("", name);
        if (str == null) {
            return Double.NaN;
        } else {
            try {
                return Double.parseDouble(str);
            } catch (NumberFormatException e) {
                return Double.NaN;
            }
        }
    }
@see nu.validator.checker.Checker#endDocument()
src/nu/validator/checker/schematronequiv/Assertions.java