!CPU - Controls the state of the IDL thread pool.
!DEBUG_PROCESS_EVENTS - Allow processing of widget events while stopped.
!DIR - Path to the main IDL directory.
!DLM_PATH - List of search paths for DLM files.
!EDIT_INPUT - Controls command-line editing.
!HELP_PATH - List of search paths for HELP files.
!JOURNAL - Contains the LUN for journal output.
!MAKE_DLL - Configure options for MAKE_DLL and CALL_EXTERNAL.
!MORE - Controls pagination for long help output.
!PATH - List of search paths for IDL routines.
!PROMPT - The text string for the prompt.
!QUIET - Print or suppress informational messages.
!VERSION - Information about the running IDL process.
!COLOR - Contains standard RGB color triplets.
!CONST - A list of physical constants.
!DPI - Double-precision value of pi.
!DTOR - Convert degrees to radians.
!FALSE - Boolean value of false (0).
!MAP - Direct Graphics map information.
!NULL - A variable of type Undefined.
!PI - Single-precision value of pi.
!RADEG - Convert radians to degrees.
!TRUE - Boolean value of true (1).
!VALUES - Contains IEEE values for Infinity and NaN.
!ERROR_STATE - The state of the last error message.
!EXCEPT - Controls how math exceptions are handled.
!MOUSE - The mouse status from the last cursor read operation.
!WARN - Controls warnings about obsolete routines and use of parentheses.
!D - State of the Direct Graphics device.
!ORDER - Controls whether Direct Graphics images are ordered top-to-bottom.
!P - State of the Direct Graphics plotting system.
!X - State of the Direct Graphics x-axis
!Y - State of the Direct Graphics y-axis
!Z - State of the Direct Graphics z-axis