Definition of Values of Property Vertical_Orientation

[Sławomir Osipiuk]

On Monday, 22 August 2022, 18:45:38 (-04:00), Richard Wordingham via 
Unicode wrote:
 >
 > The description in the file gives no assurance of that. I did,
 > however, find the necessary assurance in UAX #44 Revision 28 Section
 > 4.2.9.1.


This section, if anything, gives less assurance, by my reading.

"Complex default values other than those specified in the "@missing" line 
are explicitly listed in the relevant property file, except for instances 
noted in this section." [...] "Vertical_Orientation: This property defaults 
to Rotated (R) for most code points, but defaults to Upright (U) for 
unassigned code points in blocks associated with scripts that are 
themselves predominantly Upright, in blocks for some notational systems, 
and in blocks predominantly associated with pictographic symbols and emoji"

This implies to me that the default U values my *not* be (machine-readably) 
explicitly listed in this particular property file - why else would it be 
noted in this section? Inspecting the file, "R" is indeed listed in the 
@missing line, which leaves us with the implication that the default "U" in 
specific sections is *not* listed and must be handled specially based on 
outside information.

This seems to be a case of descriptive conceptual information appearing to 
be *imperative*.

Why is Vertical_Orientation even listed in 4.2.9.1 if it doesn't need 
special handling? How is it even a "complex" case in any meaningful way? 
The default is "R". The "U" ranges are all explicitly listed, making them 
*non-default* from a parsing standpoint, all handled by normally reading 
the data file. Is this not correct?