points to the first child of the #GNode. The other children are accessed by using the @next pointer of each child.
contains the actual data of the node.
points to the node's next sibling (a sibling is another #GNode with the same parent).
points to the parent of the #GNode, or is null if the #GNode is the root of the tree.
points to the node's previous sibling.
The #GNode struct represents one node in a [n-ary tree][glib-N-ary-Trees].