Here are the classes, structs, unions and interfaces with brief descriptions:

Comparator	Provides the capabilities to compare two objects
DataTypes
GDXMIWriter
PublicUtil
UMLAbstraction	An abstraction is a Dependency relationship that relates two elements or sets of elements that represent the same concept at different levels of abstraction or from different viewpoints
UMLAssociation
UMLAssociationEnd
UMLAttribute
UMLBehavioralFeature	A behavioral feature refers to a dynamic feature of a model element, such as an operation or method
UMLClass
UMLClassifier
UMLConstraint
UMLDataType
UMLDependency
UMLElement
UMLExpression
UMLFactory
UMLFeature
UMLGeneralizableElement
UMLGeneralization
UMLGeometry
UMLInterface
UMLMappingExpression	An expression that evaluates to a mapping
UMLModel
UMLModelElement
UMLMultiplicity
UMLMultiplicityRange
UMLName	A name is used to identify a model element uniquely within some scope
UMLNamespace
UMLOperation	An operation is a service that can be requested from an object to effect behavior
UMLPackage
UMLParameter	A parameter is an unbound variable that can be changed, passed, or returned
UMLRelationship
UMLStereotype
UMLStructuralFeature
UMLTagDefinition
UMLTaggedValue
XMIID
XMLNodeName