Re: Bidirectional editing in Emacs -- main design decisions

    Would it be sufficient to account for any arbitrary amount of
    horizontal whitespace between the beginning of the line and the
    paragraph regexps?

No, that's not correct.  You need to skip whitespace whose width is
the value of `left-margin' and then match the regexp.
(More precisely, you need to skip the amount of space
specified by the value that the function `current-left-margin' would return.)

Looking at the code, I think I was mistaken in what I said about "less
than `left-margin' indentation starts a paragraph".  I think that if
the line doesn't have `left-margin' worth of indentation, then the
paragaph regexps match at the end of the indentation.

Look at the code of `forward-paragraph' to see the paragraph criteria
in full detail.  It is very important to support the full set of
features that Emacs offers for controlling paragraphs.

At least, it is important to support the full set when this is
released.  I won't say it has to be the very next job you work on.