Allowed timezone values

I am playing with our allowed timezone settings and saw a few strange
things.  It understands "EST5EDT", but how does it understand "XYT5ABT"?test=> set timezone = 'XYT5ABT';SET
test=> SELECT current_timestamp;             now------------------------------ 2005-10-13 12:48:39.59164-04(1 row)
test=> SELECT current_timestamp + '3 months';           ?column?------------------------------- 2006-01-13
12:48:32.765068-05(1row)
 
(Shouldn't current_timestamp's label be "current_timestamp", and not
"now"?)

Also, JST doesn't work anymore, but JST9 does.  JST has no daylight
savings time values, so it is a valid timezone setting, while EST is
not:
test=> set timezone = 'JST';ERROR:  unrecognized time zone name: "JST"
test=> set timezone = 'JST9';SET

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