mattur - 10:01 pm on Jul 3, 2012 (gmt 0)
All conformant HTML parsers create an implicit tbody element in the DOM when parsing the first example. This tbody element is then available to JS and CSS because they work on the DOM, not the source code.
The whole point of Polyglot markup is to produce the same DOM when parsed as HTML or as XML, to avoid the problem of JS and CSS working differently depending on how the document is parsed. This is why the second example has an explicit tbody element, and why I chose this case as an example :)