Access command definitions

Access to the command definitions occurs during program creation time and at command run time.

To allow for syntax checking, the command must exist during the creation of a program that uses it. If it is qualified at creation time, the command needs to exist in the library referred to during creation, and in the same library when processed. If it is not library-qualified, it must be in some library on the library list during creation time and at run time.

The command name should be qualified in the program:

When the command's definition will not be accessible through the library list while the program is running.
When multiple command definitions exist with the same name if expecting a specific instance of the command at run time.

The name of the command must be the same when the program runs as when the system created it. An error occurs if the command name changes after creating a program that refers to that command. This is because the program cannot find the command when it runs. However, if a default changes for a parameter on a command, the new default is used when that command runs.