JSON is a nice way to pass complex data from my server side code to client side JavaScript. For example, in PHP I can write:

<script type="text/javascript>
    var MyComplexVariable = <?= BigFancyObjectGraph.GetJSON() ?>;
    DoMagic(MyComplexVariable);
</script>

This is pretty cool, but sometimes you want to pass more than basic date, like dates or even function definitions. There is a simple and straightforward way of doing it too, like:

<script type="text/javascript>
    var MyComplexVariable = {
        'SimpleProperty' : 42,
        'FunctionProperty' : function()
         {
             return 6*7;
         },
         'DateProperty' : new Date(989539200000),
         'ArbitraryProperty' : GetTheMeaningOfLifeUniverseAndEverything()
    };
    DoMagic(MyComplexVariable);
</script>

And this works like a charm on all browsers I've seen so far. But according to JSON.org such syntax is invalid. On the other hand, I've seen this syntax being used in very many places, including some popular JavaScript frameworks. So...

Can I expect any problems if I use "unsupported" JSON features like the above? Why is it wrong or not?