The first discussions that lead to the current formulation of the bidi
algorithm easily go back 20 years by now. There's some value in not
re-stating a specification - even if a new formulation could be found to
be 100% equivalent. That value lies in the fact that any reader can
tell, by simple inspection, that the specification hasn't changed, and
that implementations that claim conformance to earlier versions of the
specification are indeed still conformant to later versions.
This point is particularly important for the bidi algorithm, because of
it's mandatory nature and the fact that it gets re-issued with a new
version number every time that the underlying Unicode standard gets a
new version (because of new characters added, etc).
That does not preclude other, equivalent formulations of the algorithm,
whether in text books or, perhaps, as technical Note. But the burden is
on the creators of these other formulations to show that their
supposedly easier or more didactic presentation is indeed equivalent.
Having said that, there are already two other formulations of the
algorithm that are proven to be equivalent to each other (and have not
proven to deviate from the written algorithm). I'm referring of course
to the C++ (http://www.unicode.org/Public/PROGRAMS/BidiReferenceCpp/)
and Java reference implementations.
A./
PS: Personally, I don't find the presentation in terms of the regular
expressions any more intuitive than the original.
