[tz] isstd and isgmt effect

Hello all I'm writing some software that deals with dates and I parse Olson files to get time zone information. In the tzfile man page, both entries say that they are used for handling POSIX-style environmental variables? Does that mean that I can ignore those values and assume the transition times are just UAT? I couldn't find any documentation on exactly how to handle these values. The nearest thing I found was the Unix time library which seems to make an adjustment based on one setting, but it wasn't clear if this is done in general or if this was part of some specific handling. Thanks for any help you can provide. Jason