rdf:HTML datatype in RDF 1.1

Simple question on this which wasn't immediately obvious from the recommendation
[1].

Is it expected that the string has a single top-level element:

"<p>Hello world!</p>"

Or is it OK to include fragments like:

"Hello world!"
"<b>Hello</b> world!"
"Hello <i>world</i>!"
"<b>Hello</b> <i>world</i>!"

Regards,

John

[1] http://www.w3.org/TR/rdf11-concepts/#section-html