resolution of TZ variable?

I'm not sure if a consensus was ever reached on the definition of how to store information about what timezone for a user. My suggestion is that "TZ" is acknowledged as the place where the timezone choice is placed. But no definition of what the string looks like is given for POSIX. It is an implementors decision as to what is placed there -- file name, TZ rules, or magic string. On this point a "should" should be used to guide the implementor in a reasonable direction (ie one of the 3 ways listed, don't come up a 4th version). Bob Devine