See the following topics:

• Overview of External Development
• Using SPAWN and Pipes
• Using CALL_EXTERNAL()
• Remote Procedure Calls
• Types
• Keyword Processing
• IDL and Internal Variables
• String Processing
• Error Handling
• Type Conversion
• UNIX Signals
• IDL and Timers
• Files and I/O
• Miscellaneous Topics
• Adding System Routines
• Callable IDL
• Adding External Widgets to IDL
• Obsolete Internal Interfaces