That’s an internal method, not intended to be called by the user. I’m not sure why it appears in the generated docs page.
To make a new config variable, just create an instance of whatever type of config variable you need, e.g. ConfigVariableString(‘my-config-variable’, ‘default-value’). See this page in the manual.
The method you describe wasn’t working earlier, but it works fine now. I must have opened the wrong PRC file when I was testing this earlier. Thank you for the help!