For some cases (extracting a portion of a document's tree, creating a new fragment of a document, inserting nodes as children
of another node) it is desirable to have an object which can hold fragments of document. Document
object itself is a little bit heavyweight for this, something lightweight that behaves like Node
is much better. And exactly this is DocumentFragment
[When a DocumentFragment is inserted into a Document (or indeed any other Node that may take children) the children of the DocumentFragment and not the DocumentFragment itself are inserted into the Node.