UTC/1999-023
Date: 6-9-99
Progressing TR#9 Bidi Algorithm
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After the UTC approved changes to TR#9 Mark edited and posted a version 4.0
of the TR on the web. In the months following UTC#79 great progress has been
made in comparing two independently created implementations for
compatibility and conformance.
Since then the bidi committee has discovered that the algorithm as stated
does not meet one
of the original goals of supporting a style based implementation (see
below). This is important since use of bidi in markup would involve such
implementations.
Several (limited) revisions of certain parts of the algorithms related to
the handling of explicit bidi controls have been proposed to overcome the
limitiations discovered. (Two versions of these are available as documents
L2/99-171 and L2/99-171R). These are being reviewed by the bidi committee.
As a result of these changes, it's currently not possible to achieve the
same level of verification as had been achieved for the previous version of
the algorithm, and it's not possible for UTC to ratify a final text at this
meeting.
Therefore, Mark, Ken, Lisa and Asmus met and agreed to propose the following
plan of action for UTC.
1) TR#9 Version 4.0 will be used as the starting place for editing the book
2) UTC approves (reaffirms) these goals
- the bidi algorithm will produce the same result wether implemented
using explicit formatting codes in the text stream or whether used in
a style based way, where explicit levels are supplied externally.
- either style of implementations can be implemented with reasonable
bounds of complexity, in particular, it can be demonstrated that
the correct results can be achieved
a) by the style based implementation without inserting explicit
codes into the stream
b) by the implementation using formatting codes without physically
removing them
- the bidi algorithm is verified by demonstrating that two independly
created implementations produce the same results
3) The bidi committee is charged to define the change in language relative
to the
base text of step (1) that is needed to make the algorithm meet the
goals set forth
above and to verify that the algorithm meet these goals.
4) Mark Davis is appointed 'rapporteur' for the bidi committee and has the
responsibility
to coordinate the work of the bidi committee, collect the results and
provide the final
text to the editorial committee.
5) If a new stable formulation of the algorithm acceptable to the bidi
committee
can be developed and verified (as above) in time for the copy editing
of the book,
the editorial committee is empowered to use it for the book.
Otherwise, the
editorial commitee will use the existing (Version 4) of the algorithm
as fallback
for publication.
Member companies with interest and experience in bidi implementations are
invited
to participate in the work of the bidi committee.