[clock scan] weirdness

OK, I'm just kinda baffled by all this:

(Tcl) 54 % puts $tcl_patchLevel
8.4.12
(Tcl) 55 % clock format [clock scan "2005-08-05 14:20:09"]
Fri Aug 05 2:20:09 PM Pacific Standard Time 2005
(Tcl) 56 % clock format [clock scan "2005-08-05 14:20:09 +1"]
unable to convert date-time string "2005-08-05 14:20:09 +1"
(Tcl) 57 % clock format [clock scan "2005-08-05 14:20:09 i1"]
Sun Aug 05 4:20:09 PM Pacific Standard Time 2001
(Tcl) 58 % clock format [clock scan "2005-08-05 14:20:09 -1"]
Fri Aug 05 7:21:09 AM Pacific Standard Time 2005
(Tcl) 59 % clock format [clock scan "2005-08-05 14:20:09 x1"]
Sat Aug 04 8:20:09 PM Pacific Standard Time 2001
(Tcl) 60 % clock format [clock scan "2005-08-05 14:20:09 - 1 hour"]
Fri Aug 05 8:21:09 AM Pacific Standard Time 2005
(Tcl) 61 % clock format [clock scan "2005-08-05 14:20:09 + 1 hour"]
Fri Aug 05 3:20:09 PM Pacific Standard Time 2005

I'm sure there's a rational explanation why 14-1=8 and why "-1" and
"x1" and "i1" are allowed but "+1" isn't and why "-1hour" subtracts
5:59 while "-1" subtracts 6:59 and why "i1" adds two hours but
subtracts 4 years and so on but... I sure as hell don't see the
pattern...

And on a more practical note: is there a way to hand [clock scan] a
time spec like 14:20:09-400 and have it actually understand that this
identifies a time zone?

cordially

Y.T.

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