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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 fulfil 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 insertBefore()
and appendChild()
.
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