The parent node into which the part renders its content.
A ChildPart's content consists of a range of adjacent child nodes of
.parentNode, possibly bordered by 'marker nodes' (.startNode and
.endNode).
If both .startNode and .endNode are non-null, then the part's content
consists of all siblings between .startNode and .endNode, exclusively.
If .startNode is non-null but .endNode is null, then the part's
content consists of all siblings following .startNode, up to and
including the last child of .parentNode. If .endNode is non-null, then
.startNode will always be non-null.
If both .endNode and .startNode are null, then the part's content
consists of all child nodes of .parentNode.
The part's leading marker node, if any. See .parentNode for more
information.
OptionaldirectiveParent: DirectiveParent
The part's trailing marker node, if any. See
.parentNodefor more information.