<> <> <<1. Extension mechanisms (example of object style)>> <<1. recast; class mechanism>> <<2. extract procs>> <<3. layout procs>> <<1. Principles>> <> 1. Object style for extension 2. properties for extension 3. code eqv. schematics (link to interpretation) 4. computation model especially to produce layout 5. interactive user interface speed of response talk in terms of source 6. capture high level abstractions 7. orthogonal implementations of orthogonal concepts; wired together tool integration layered system