Re: Need for Level Direction Mark

On Mon, 19 Sep 2011 05:44:27 +0200
Philippe Verdy <verdy_p_at_wanadoo.fr> wrote:

> 2011/9/19 Peter Edberg <pedberg_at_apple.com>:

> > <snip> The whole point
> > of LDM was to be able to create semi-structured elements such as
> > the example in UAX #9 section 5.6 *without* knowing in advance
> > the direction context in which the element would be used.
>
> You absolutely don't need to know in advance the direction of context
> before using LRE..PDF or RLE..PDF. It will work in both directions,
> ordering and separating the fields in the same order as this context.
> So yes LRE..PDF and RLE..PDF create a semi-structure, which does fit.

Actually, no. A sequence <LRE embedded_1 PDF N LRE embedded_2 PDF>
will result in N being resolved as L by rule N1. Consequently
embedded_1 will display to the left of embedded_2 whatever the
context. You still need something like <LRE embedded_1 PDF RLM N LRE
embedded_2 PDF> to force embedded_1 to display before embedded_2
whichever the directionality of the embedding within which these
occur. (DLM could substitute for RLM and avoid untidily placed
non-rendering runs.) Alternatively, you could alternate LRE...PDF and
RLE...PDF.

You also need extra marks to avoid the structure sucking in adjacent
elements - you need either

<RLM LRE embedded_1 PDF RLM N LRE embedded_2 PDF RLM>

or

<DLM LRE embedded_1 PDF DLM N LRE embedded_2 PDF DLM>

Actually, I suppose you might benefit from replacing the final mark
above by an ALM.

Using embeddings has the advantage that one doesn't have to worry about
Arabic or European numbers.

Richard.
Received on Mon Sep 19 2011 - 17:56:18 CDT