[The UNIX command line is a success story of software extensibility because it efficiently allows for infinite combinations of smaller programs to create a workflow.]
[The spreadsheet and scratch do not require mental abstractions because the workings of the program are made apparent through visual embodiment.]
[The spreadsheet and the developer tools console shorten the save/build/run loop until it no longer exists, thus allowing someone to interact with a living system that responds in real-time.]
[In-place tool-chains allow users to leverage familiar concepts from everyday use and extend their experience.]