HP 4 FAMILY - Manual (Page 138)

The new algorithm for deciding whether or not to
counter-rotate characters (when using the Character Text
Path Direction command’s vertical-rotated printing mode)
is as follows:
if (the current font contains a VE segment)
{
if(the character code* is NOT contained in
a VE range)
rotate
else
don’t rotate
}
else
use the old logic
* The original character code, even if a galley character
were substituted at some point.
Examples:
Japanese ShiftJIS Japanese Unicode
Segment ID V E V E
Format/NumRanges 0 1 0 2
Range1FirstCode 0x0000 0x0000 half-width latin
characters
Range1LastCode 0x00FF 0x007F
Range2FirstCode 0xFF61 half-width
katakana
Range2LastCode 0xFF9F
2-102 Printer-Specific Differences