Hello, I have written a timezone library (including a parser) in JavaScript and am running into a bit of confusion with this particular Zone and Rule: # Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S Rule Salv 1987 1988 - May Sun>=1 0:00 1:00 D Rule Salv 1987 1988 - Sep lastSun 0:00 0 S # There are too many San Salvadors elsewhere, so use America/El_Salvador # instead of America/San_Salvador. # Zone NAME GMTOFF RULES FORMAT [UNTIL] Zone America/El_Salvador -5:56:48 - LMT 1921 # San Salvador -6:00 Salv C%sT My question is, what is the applicable Rule for any date after 1988? The last "Salv" Rule ends in 1988, and the Zone states that Salv is the Rule from 1921 on (no UNTIL specified) I've done a "man zic" hoping to see something like "If there is no applicable Rule, just use the basic offset and assume that the LETTER is 'S'", but I could not find anything like that. Is that the correct behavior? Thanks Bobby