This is the abstract base class for each state element whose value is replaced whenever it is set. (Most state elements fall into this category, so most are derived from this class.)

This class overrides the SoElement.getElement() method to store the node-id of the node that is about to set the value in the element (i.e., the node that is passed to getElement()). This class also defines the SoElement.matches() method to return true if the node-id's of the two elements match. Subclasses can change this behavior by defining matches() differently, if they wish. For example, they can compare the elements' values, instead.

Reference