Add Custom Properties to a PropertyGrid

<?xml version="1.0" encoding="utf-8" ?>
<bookstore>
	<book genre="autobiography" publicationdate="1981" ISBN="1-861003-11-0">
		<title>The Autobiography of Benjamin Franklin</title>
		<author>
			<first-name>Benjamin</first-name>
			<last-name>Franklin</last-name>
		</author>
		<price>5.90</price>
	</book>
	<book genre="novel" publicationdate="1967" ISBN="0-201-63361-2">
		<title>The Confidence Man</title>
		<author>
			<first-name>Herman</first-name>
			<last-name>Melville</last-name>
		</author>
		<price>11.90</price>
	</book>
	<book genre="philosophy" publicationdate="1991" ISBN="1-861001-57-6">
		<title>The Gorgias</title>
		<author>
			<first-name>Sidas</first-name>
			<last-name>Plato</last-name>
		</author>
		<price>9.90</price>
	</book>
</bookstore>