<itemvalue="A visitor that will recursively visit all of the element in an element model. For example, using an instance of this class to visit a [CompilationUnitElement] will also cause all of the types in the compilation unit to be visited. Subclasses that override a visit method must either invoke the overridden visit method or must explicitly ask the visited element to visit its children. Failure to do so will cause the children of the visited element to not be visited. Clients may extend this class."/>
<itemvalue="A visitor that will do nothing when visiting an element. It is intended to be a superclass for classes that use the visitor pattern primarily as a dispatch mechanism (and hence don't need to recursively visit a whole structure) and that only need to visit a small number of element types. Clients may extend this class."/>
<itemvalue="An object that can be used to visit an element structure. Clients may not extend, implement or mix-in this class. There are classes that implement this interface that provide useful default behaviors in `package:analyzerdartelementvisitor.dart`. A couple of the most useful include SimpleElementVisitor which implements every visit method by doing nothing, RecursiveElementVisitor which will cause every node in a structure to be visited, and ThrowingElementVisitor which implements every visit method by throwing an exception."/>
