Re: Bidirectional text and URLs

[Richard Stallman <rms@gnu.org>]

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To be able copy some text into another buffer and have that text
display there just as it displayed in the original buffer is important
for user messages about what's going on with bidi.

I think it requires two facilities.  (Please correct me if I'm wrong.)

1. A way for a Lisp program to get, for a specified region, a
short description of the outside bidi context that affects bidi
treatment of that region.

The result should be a small amount of data, computed solely from the
text outside the specified region.  The result should encapsulate
everything about the text outside the specified region that can
possibly affect the bidi treatment of whatever text might be inside
the region.

Thus, any change in the text outside the specified region, which gives
the same encapsulated data, will not affect bidi treatment of text
inside the region.

Ideally, this data should have a transparent documented format.

It could be called 'bidi-context'.

If this can't be done in a way that is independent of the text inside
the specified region, as a fallback it could be done in a way that
works only for the current text inside that region.

2. Given such encapsulated context data, a straightforward way to
create an equivalent bidi context in the current buffer.  I expect it
would work by inserting some magic bidi characters.  (Can all such
contexts be replicated by inserting some magic bidi characters?)

It could be called 'replicate-bidi-context'.

Are these feasible to implement?

-- 
Dr Richard Stallman
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