UAX #9: applicability of higher-level protocols to bidi plaintext

Ken Whistler via Unicode unicode at
Wed Jul 18 09:36:48 CDT 2018

On 7/18/2018 6:43 AM, philip chastney via Unicode wrote:
> there are also contexts where "Hello World!" can be read as
> the function "Hello", applied to the factorial value of "World"
> even though such a move wouldn't necessarily remove all ambiguity,
> the easiest solution is to declare that formal notations cannot be "plain" text

Of course they can -- and (usually) should be, as they are designed that 
way. To state otherwise would just create headaches for designing 
parsers for formal notations.

I think you are confusing ambiguity of *interpretation* of bits of 
formal notation, taken out of context, with ambiguity of *display* of 
formal notations in contexts where one does not know and control the 
paragraph directionality.

The easiest (and correct) solution, when displaying formal notation for 
visual interpretation by human readers, is to use tools where one knows 
and can rely on the paragraph directionality explicitly, so that Unicode 
bidi doesn't add an out-of-left-field set of display conundrums, as it 
were, for bidi edge cases that can result in *mis*interpretation by the 

In other words, if I am trying to read C program text or regex 
expressions, I expect that my tooling is not going to silently assume a 
RTL paragraph directional context and present me with visual garbage to 
interpret, forcing me to reverse engineer the bidi algorithm in my head, 
just to read the text. Why would I put up with that?


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