Although any text editor can be used to create an IDL program file, the IDL Editor included in the IDL Development Environment contains features that simplify the process of writing IDL code. For example, if you indent a line using the Tab key, the following lines will be indented as well.
If you use the IDL Development Environment, files are opened in the IDL Editor by default. On UNIX platforms, you can simplify the process of using another editor; see Using External Editors (Motif) for details.
If you have a file open in the IDL Editor and you modify the file using another editor (on any platform), IDL will warn you that the file in the IDL Editor window has changed, and give you a chance to reload the file.