The product uses configuration variable files to get values for settings that vary from system to system and from user to user.

For example, the product needs to find its main resource file, which can be defined by the configuration variable MS_RSRC in the configuration variable file. Rather than always looking for a file named ustation.rsc in a specific directory, the program expands the configuration variable MS_RSRC to get a filename and location. That way, the program finds the file regardless of its name and location.

Each configuration variable has two parts: its name and its definition. Variable definitions can be literal strings or combinations of strings and references to other variables.

When the program needs the value of a variable, it looks in the variables table (kept in memory) to find the definition. If the variable is found, it then expands any nested variable references in the definition. If the variable cannot be found, it then attempts to find an operating system environment variable of the same name. If an operating system environment variable is defined, the program uses that value as if it were defined in the variables table.