BidiMirrored property and ancient scripts (Was Re: Plain text custom fraction input)

[Eli Zaretskii]

> Date: Fri, 24 Jul 2015 21:23:52 +0100
> From: Richard Wordingham <richard.wordingham at ntlworld.com>
> 
> On Fri, 24 Jul 2015 10:09:18 -0700
> Asmus Freytag <asmusf at ix.netcom.com> wrote:
> 
> > On 7/24/2015 2:59 AM, Frédéric Grosshans wrote:
> > > Let me rephrase my remark in a less “stupid and dangerous” way.
> > >
> > >    If a LTR character has the BidiMirrored=No property, it may
> > > either be mirrored or not when typeset in RTL, depending on other
> > > factors. Specifically, the BidiMirrored property has not been
> > > specified for ancient LTR scripts which are mirrored when RTL or
> > > boustrephodon, like Italic, Runic, Archaic Greek, Archaic Latin,
> > > Egyptian Hieroglyphs. Note that some RTL script, like Old North
> > > Arabian, are mirrored when LTR. 
> 
> > We do want "BidiMirrorred=No" to be honored; for example for the
> > arrows and the ornate parens. And we do not want that to be overridden
> 
> And at present, that may be overridden in a right-to-left context!

What do you mean by "overridden" in this context?  AFAIK, mirroring
indeed depends on context, but a character whose BidiMirrorred
property is No will _never_ be mirrored, according to the UBA.  There
are no overrides for that property, AFAIK.