strlst/IN Changes and New SUBSET/INTERSECT Operators

In Texis version 7, significant strlst and IN operator behavior was changed, and a few new strlst operators were added. The following is an overview of the changes; see the Texis manual section on IN, SUBSET and INTERSECT for further details and syntax. These changes (except for the new operators SUBSET and INTERSECT) can be rolled back with <vxcp compatibilityversion 6>.