Add an object that will be notified of the changes to this node and its descendants.
The difference between adding a regular observer and a subtree observer is that the subtree observer will also be notified if a change occurs to any of the node's descendants, while a regular observer will only be notified of changes to the node it was assigned to.
|observer||The observer object|
Implemented in Inkscape::XML::SimpleNode.
Referenced by Inkscape::Preferences::addObserver().