Here is how BeanShell's author, Pat Niemeyer, describes his creation:
You do not have to know anything about Java to begin writing your own jEdit macros. But if you know how to program in Java, you already know how to write BeanShell scripts. The major strength of using BeanShell with a program written in Java is that it allows the user to customize the program's behavior using the same interfaces designed and used by the program itself. BeanShell can turn a well-designed application into a powerful, extensible toolkit.
This guide focuses on using BeanShell in macros. If you are interested in learning more about BeanShell generally, consult the BeanShell web site. Information on how to run and organize macros, whether included with the jEdit installation or written by you, can be found in Chapter 8, Using Macros.