Focus on extensibility
- Emacs was built with focus on extensibility from the very beginning.
Demand for extensibility
- Because Emacs has reputation of being extensible, most people expect extensibility from Emacs and Emacs modes. This makes authors add options to customize behavior that nobody normally adds.
- Emacs Lisp makes it easy to redefine or patch any function
Emacs is self-describing
- Emacs allows exploring itself: extensive documentation for most functions, Emacs allows looking up documentation, jump to definition, etc.
- Open Source