6.9. Semi-standards [CMS] A set of extensions that stems from the VM/CMS operating system. Basically, this includes the most common extensions in the VM/CMS version of REXX, in addition of some functions that perform task normally done with commands under VM/CMS. [VMS] A set of interface functions to the VMS operating system. Basically, this makes the REXX programming under VMS as powerful as programming directly in DCL. [UNIX] A set of interface functionality to the Unix operating system. Basically, this includes some functions that are normally called as commands when programming Unix shell scripts. Although it is possible to call these as commands in Regina, there are considerable speed improvements in implementing them as built-in functions.