Returns a builder for constructing changes to the named child node. If the named child node does not already exist, a new empty child node is automatically created as the base state of the returned child builder. Otherwise the existing child node state is used as the base state of the returned builder.
All updates to the returned child builder will implicitly affect also this builder, as if a {@code setNode(name, childBuilder.getNodeState())} method callhad been made after each update. Repeated calls to this method with the same name will return the same child builder instance until an explicit {@link #setChildNode(String,NodeState)} or{@link #remove())} call is made, at which point the linkbetween this builder and a previously returned child builder for that child node name will get broken.
@since Oak 0.6
@param name name of the child node
@return child builder