The document discusses how the UML2Tools project used the Eclipse Graphical Modeling Framework (GMF) to develop UML diagram editors. It describes how GMF generates a core diagram editor but requires customization for specific features. The UML2Tools editors posed an extensive test for GMF due to the complexity of UML modeling. It augmented GMF through custom code, dynamic templates, and extending the GMF metamodel to support sophisticated domain to diagram mapping, different levels of detail, switching element notations, and diagram-on-diagram capabilities for UML modeling.