DocumentFragment is a "lightweight" or "minimal"
Document object. It is very common to want to be able to
extract a portion of a document's tree or to create a new fragment of a
document. Imagine implementing a user command like cut or rearranging a
document by moving fragments around. It is desirable to have an object
which can hold such fragments and it is quite natural to use a Node for
this purpose. While it is true that a Document object could
fulfill this role, a Document object can potentially be a
heavyweight object, depending on the underlying implementation. What is
really needed for this is a very lightweight object.
DocumentFragment is such an object.
Furthermore, various operations -- such as inserting nodes as children
of another Node -- may take DocumentFragment
objects as arguments; this results in all the child nodes of the
DocumentFragment being moved to the child list of this node.
The children of a DocumentFragment node are zero or more
nodes representing the tops of any sub-trees defining the structure of
the document. DocumentFragment nodes do not need to be
well-formed XML documents (although they do need to follow the rules
imposed upon well-formed XML parsed entities, which can have multiple top
nodes). For example, a DocumentFragment might have only one
child and that child node could be a Text node. Such a
structure model represents neither an HTML document nor a well-formed XML
document.
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. This makes the DocumentFragment very
useful when the user wishes to create nodes that are siblings; the
DocumentFragment acts as the parent of these nodes so that
the user can use the standard methods from the Node
interface, such as Node.insertBefore and
Node.appendChild.
See also the Document Object Model (DOM) Level 3 Core Specification.