RE: Proposal for isolation characters in Unicode and the unicode-bidi:isolate and unicode-bidi:plaintext definitions

I am late joining this discussion, because I did not see really compelling arguments in favor of option 1 rather option 2 or vice versa.

Just to add to the fun, I want to suggest a third option: in the case of improperly  nested embeddings/overrides/isolates, both PDF *and* PDI will close all unmatched controls.

Going back to examples a and b:




In example a, the PDI will close the RLI and the LRE, PDF does nothing.

In example b, the PDF will close the LRI and the RLE, PDI does nothing.

If nothing else, this option has the merit of symmetry.

However, I am not in mad love with it, and I can live with either one of 1 or 2.



Shalom (Regards),  Mati


From: Glenn Adams [] 
Sent: Monday, July 09, 2012 5:07 PM
To: Aharon (Vladimir) Lanin
Cc: Martin J. Dürst; W3C style mailing list;
Subject: Re: Proposal for isolation characters in Unicode and the unicode-bidi:isolate and unicode-bidi:plaintext definitions



On Mon, Jul 9, 2012 at 12:28 AM, Aharon (Vladimir) Lanin <> wrote:

> I don't understand your logic. You say option 2 offers greater forward compatibility,

> but then say you are choosing 2 because forward compatibility is NOT important.


Not because it isn't important, but because in certain cases is LESS important than another consideration. It's a trade-off.


In other words, I think that well-formed documents, i.e. ones where isolates and embeddings/overrides are properly nested, should display as well as possible on systems that do not support isolates. That is why the proposal has been modified to include PDI. On the other hand, when it comes to essentially broken documents, where embeddings/overrides and isolates are not properly nested, I think it is more important to let isolates do their job and isolate the missing and extra PDFs in the apps that do support isolates than to make the document display as similarly as possible on old and new apps, when apps that don't understand isolates can't possibly display the document 100% as intended anyway.


> I think backward compatibility is more desirable, i.e., a system that knows nothing of

> isolates should work without modification,


By definition, it can't display the document 100% as intended. We introduce PDI is so its disability is limited to displaying isolates incorrectly (but then limit this to when isolates and embeddings/overrides are properly nested).


> and yet option 2 requires PDI to close an embedding/override,


Only when the isolate began before the embedding/override. If we have LRE RLI PDI PDF, the PDI only closes the isolate, not the embedding.


That stills leaves that case where pre-PDI implementations would behave differently than PDI aware implementations, since the former would not close the embedding/override at the same position. I believe that may be a problem, and should be avoided.

Received on Friday, 20 July 2012 16:22:35 UTC