[UA-discuss] Programming Language Hacks - UA103

[Andrew Sullivan]

On Wed, Aug 09, 2017 at 04:13:35PM +0000, Mark Svancarek via UA-discuss wrote:
> Actually, we recently discovered an Edge bug (via the browser review) where the order of labels in a RTL.RTL.ASCII domain name were transposed during rendering.  So I like calling it out explicitly.
> 

This has been a regularly-recurring bug in various rendering engines
since at least 2008, because I recall the demonstrations of it during
the idnabis WG, and then seeing it in a completely different context
during the VIP work for ICANN in 2011 or '12.  It's not always only
Arabic: at least one of the examples was reproducible in any bidi
context.  I seem to recall one example where the wire order

    [firstlabel]RTL[secondlabel]RTL[thirdlabel]LTR[fourthlabel]NULL

got rendered as

    RTL.LTR.RTL

Which I thought was a pretty cool bug.  I have no idea how it happened
that way, though I recall walking mysef through the bidi algorithm at
the time and figuring out what the problem must have been.  Bidi is
hard.

I therefore think it wise not to call out Arabic especially -- but
maybe point out that Arabic is perhaps the most prominent writing
system that uses RTL, so that programmers aren't tempted to dismiss
the problem as a "corner case".  Big corner, the Arabic-using
population!

Best regards,

A

-- 
Andrew Sullivan
ajs at anvilwalrusden.com