Unclear text in the UBA (UAX#9) of Unicode 6.3

[Eli Zaretskii]

> Date: Thu, 24 Apr 2014 00:28:50 -0700
> From: Asmus Freytag <asmusf at ix.netcom.com>
> CC: ken at unicode.org, Eli Zaretskii <eliz at gnu.org>, 
>  James Clark <jjc at jclark.com>,
>  unicode Unicode Discussion <unicode at unicode.org>
> 
> On 4/23/2014 7:37 PM, Philippe Verdy wrote:
> > Thanks for the clear reply, now I know that my example in a prior 
> > message would work appropriately with UBA:
> >
> >   This is an [«] ARABIC EXAMPLE [»] for demonstration only.
> >
> > Because:
> > - the opening guillemet is not stripped out of the context stack when 
> > the first closing bracket is matched with the first opening bracket,
> This is _*incorrect*_, see the text in blue/bold in the definition 
> copied below.
> The second bullet in item 3 of the second second-level bullet of the 
> third top-level bullet of BD16 clearly says that all elements that are 
> above the matched element are popped together with it.
> > - later the closing guillemet matches the opening guillemet remaining 
> > on the stack,
> No, this is_*incorrect*_, because the stack has been popped.

Indeed.

In addition, assuming that by "guillemets" Philippe means U+00AB and
U+00BB, they cannot possibly form a bracketed pair, because their
General Category is not Ps and Pe.  For that reason, you will never
find them in BidiBrackets.txt.