An include file is a Studio document that contains definitions for ObjectScript macros. See “ObjectScript Macros and the Macro Preprocessor” in Using Caché ObjectScript.
You create include files in Studio; see Using Studio.
Includes the following class methods that you can use with include files:
Availability: All namespaces.
The special variable $SYSTEM is bound to the %SYSTEM package. This means that (for ObjectScript) instead of ##class(%SYSTEM.class).method(), you can use $SYSTEM.class.method().