Most of the GNU Emacs integrated environment is written in the programming language called Emacs Lisp. The code written in this programming language is the software-the sets of instructions-that tell the computer what to do when you give it commands. Emacs is designed so that you can write new code in Emacs Lisp and easily install it as an extension to the editor. (GNU Emacs is sometimes called an "extensible editor," but it does much more than provide editing capabilities. It is better to refer to Emacs as an "extensible computing environment." However, that phrase is quite a mouthful. It is...

Texinfo is a documentation system that uses a single source file to produce both online information and printed output. This means that instead of writing two different documents, one for the online information and the other for a printed work, you need write only one document. Therefore, when the work is revised, you need revise only that one document. Texinfo's markup commands are almost entirely semantic; that is, they specify the intended meaning of text in the document, rather than physical formatting instructions. Texinfo was devised for the purpose of writing software documentation and...