[Q] Bidirectional Algorithm

From: Jonathan Rosenne (100320.1303@CompuServe.COM)
Date: Wed Nov 13 1996 - 19:42:57 EST


Kent Johnson wrote:
>1. In step T6, why are implicit directional formatting codes (RLM and LRM,
>according to the description on p 3-15) removed?

I guess it means RLE and LRE, not LRM and RLM. See the preceding line.

>2. Do sot/eot refer to start and end of an embedding level, or only the start
>and end of the entire block being processed? If only to the start and end of
the
>block, what is the behavior of the algorithm in steps P0 and N1-N3 when a level
>change is detected?

sot and eot refer to the entire text being processed, i.e. up to the block
separator. The P0 question pertains to Arabic, so I cannot answer it. N2 clearly
defines the effect of sot and eot on neutrals.

>4. In step I1, should this read, "Numeric text (EN) goes up two levels unless
>preceeded by left-to-right text AT THE SAME EMBEDDING LEVEL"? If so, then what
>happens to an EN at the beginning of an embedding level? What if the first
>character after sot is EN?

In both cases it is not preceded by l2r text so I1 does apply.

>5. Do quote marks and parentheses affect the embedding level in a special way?
>There is no mention of these characters in the algorithm, and their character
>type is "Other neutral" in UNIDATA2, but ALL of the examples containing quote
>marks on pp 3-20 and 3-21 seem to require either special handling of single and
>double quotes, or use of explicit embedding codes.
>
>For example, on page 3-21:
>Memory: he said "car MEANS CAR."
>Resolved levels: 000000000222111111111100

>Why is car at level 2? If quote has no special meaning, car should be at level
>0. On the other hand, if quote is interpreted as pushing a level, then why is
>the period at level 0 instead of level 1? The only way I can duplicate this
>result is to insert a LRE between quote and car, and a PDF between CAR and
>period.

The example shows the memory and resolved levels at this stage. The LRE etc.
were removed in T6. Obviously there had been either an LRE or an LRO.

>7. An observation: In step N3, the sequences R N EN N R and R N EN N L should
>never occur because in step P0 they resolve to R N AN N R and R N AN N L
>respectively.

P0 applies only to Arabic.

Jonathan Rosenne
JR Consulting
P O Box 33641, Tel Aviv, Israel
Phone: +972 50 246 522 Fax: +972 9 956 7353
http://ourworld.compuserve.com/homepages/Jonathan_Rosenne



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