Clojure Mode
Note that the mode line for the project.clj buffer in the screenshot below displays (Clojure) indicating that the clojure-mode major mode is enabled. When a file with an extension recognized as a Clojure file type is opened, Emacs sets the major mode of the buffer to clojure-mode.
Screenshot - project.clj

The main Clojure file extensions are:
| Extension | Content |
|---|---|
| .clj | Clojure Code |
| .cljs | ClojureScript Code |
| .edn | EDN data (similar in concept to JSON) |
clojure-mode provides the core Clojure language support. This includes:
- Syntax Highlighting (a.k.a. "font locking" in Emacs-speak)
- Indentation
- Refactoring
- REPL Integration
FYI
- clojure-mode and CIDER are distributed as separate Emacs packages but are maintained by the same author. The clojure-mode package is a dependency of CIDER but may be used independent of CIDER (e.g. to use in conjuction with the inf-clojure, an alternative Clojure REPL package).
- CIDER appends entries to the Emacs
auto-mode-alistvariable to enableclojure-modefor supported Clojure file types.