What about the idea of using the notation </qname/>expression to indicate a singleton element that automatically terminates when any other tag is encountered:
<book:book>
</book:author/>John Grisham
</book:title/>The Firm
</book:book>
White space would be ignored automatically. This would be very useful for inputting data-centric content into an XML document, and also is visually suggestive of regex terminology.