Provide samples of well-known, complexer domains

[learn-more]

An example for a well-known domain (for example, xml) would be very helpful.
The idea of xml is fairly simple, but the domain is actually pretty complex.

Without understanding everything, I gobbled together something like this:

auto XmlOpenTag() {
    return InRegexp("<[^(/><.)]+>");
}

auto XmlCloseTag() {
    return InRegexp("</[^(/><.)]+>");
}

auto XmlEmptyTag() {
    return InRegexp("<[^(/><.)]+/>");
}

FUZZ_TEST(XMLTest, XMLReadFromStringHasNoUndefinedBehavior)
    .WithDomains(OneOf(XmlOpenTag(), XmlCloseTag(), XmlEmptyTag(), Arbitrary<std::string>()))
    .WithSeeds([]() -> std::vector<std::tuple<std::string>> {
        return {
            { "<tag></tag>" },
            { "<tag><tag></tag></tag>" },
            { "<tag><tag>garbage</tag></tag>" },
            { "<tag><tag stuff=\"xxxxx\">garbage</tag></tag>" },
            { "<tag><tag><tag /></tag></tag>" },
        };
    });

But this is far from a decent implementation.