To extend jed, it is necessary to become familiar with the S-Lang
programming language. S-Lang not a standalone programming language like
C, Pascal, etc. Rather it is meant to be embedded into a C program. The
S-Lang programming language itself provides only arithmetic, looping, and
branching constructs. In addition, it defines a few other primitive
operations on its data structures. It is up to the application to define
other built-in operations tailored to the application. That is what has
been done for the jed editor. See the document slang.txt for
S-Lang basics as well as the jed Programmer's Manual for functions jed has
added to the language. In any case, look at the *.sl files for
explicit examples.
For the most part, the average user will simply want to rebind some keys and change some variables (e.g., tab width). Here I discuss setting keys and the predefined global variables.