Re: Bidirectional editing in Emacs -- main design decisions

[Eli Zaretskii <eliz@gnu.org>]

> Date: Fri, 09 Oct 2009 23:18:00 +0200
> From: Eli Zaretskii <eliz@gnu.org>
> Cc: 
> 
>    So I decided to use such a higher protocol -- namely,
>    the Emacs definition of a paragraph, as determined by the
>    `paragraph-start' and `paragraph-separate' regexps.

A small, but significant correction to this: these two regexps are
looked for anchored at line beginning.

The reason for this deliberate deviation from the letter of Emacs
definition of a paragraph are complicated, but the upshot is that from
the user point of view, it does not make sense to change paragraph
direction if the paragraph separator does not begin at the beginning
of a line.

As another deviation from the definition of a paragraph, text that
matches `paragraph-separate' is given the same direction as the
preceding paragraph.  (By contrast, Emacs generally does not consider
`paragraph-separate' as part of any paragraph.)