Learn about Dreamweaver extensions.
Most Dreamweaver extensions are written in HTML and JavaScript. This guide assumes that you are familiar with Dreamweaver, HTML, XML, and JavaScript programming. If you are implementing C extensions, the guide assumes that you know how to create and use C dynamic link libraries (DLLs). If you are writing extensions for building web applications, you should also be familiar with server-side scripting on at least one platform, such as Active Server Pages (ASP), ASP.NET, PHP: Hypertext Preprocessor (PHP), Adobe® ColdFusion®, or JavaServer Pages (JSP).
Download the complete Extending Adobe Dreamweaver CS5 and CS5.5 Extensions guide.