I'm not sure why you're having trouble with that, because you can use the expressions panel to see a list of all variables you can use, and you can also set a comment on individual variables which is also displayed beside the variable. Doesn't that do what you want? Combined with ordinary comments (press Q), surely you can have comprehensive documentation all through your project? Failing that, some notes in NotePad couldn't hurt.
Alternatively you might want to use the Dictionary object instead of Array. If you're looking up the rank name associated with a number or code, that's much better suited to Dictionary lookups than Array.