[emacs-bidi] Re: Callbacks?

[Martin Duerst]

At 05:59 05/12/01, Eli Zaretskii wrote:
>> Date: Wed, 30 Nov 2005 16:50:57 +0900
>> From: Martin Duerst <address@hidden>
>> Cc: address@hidden
>>
>> Where and how the cursor should be displayed, which physical
>> direction it moves for cursor keys such as -> or <-, whether
>> selection is logical or visual, and so on.
>
>This was all discussed here some time ago, please be sure to read the
>list archives.

Can you give me a pointer, e.g. to some specific message or
to the approximate date?

>We've come to some conclusions which should be evident
>from the discussions.
>
>But really, these are all secondary issues: we have a long and bumpy
>road ahead before we are ready to become bothered by how to move the
>cursor.

I agree. I just mentioned these because you seemed to say that
all editors should do exactly the same thing re. bidi, and
I wanted to show an example where this wasn't the case.

>>  >That said, this is Emacs we are talking about; all the relevant
>>  >character properties are loaded into internal data structures, so
>>  >there should be no problem, in principle, to fiddle with them for a
>>  >particular mode.
>>
>> Good to know. The following are potential problems:
>> - Can the properties be set for each mode individually?
>
>Yes: the tables can be made buffer-local.

Okay, great.

>> - Can the properties change based on context?
>
>No, since the tables are global for displaying all parts of the
>buffer.
>
>>    As a simple
>>    example, attributes in XML can be quoted with single quotes
>>    or with double quotes. In the attribute value, the 'other'
>>    quote can then be used literally. So if we have something
>>    like
>>    <element attr1="What's up?" attr2='He cried "Help!" and ran away.' />
>>                   1    2     1       1         2     2              1
>>    then for the places marked 1, which are XML syntax, we want to
>>    change the properties (e.g. to LTR), but for the cases marked
>>    with 2, which are content, we do not want to change the properties.
>>    Would such a thing be possible?
>
>Not via fiddling with character properties.  We will have to come up
>with some different solution.

Okay, I see.

>> - In our current approach, we not only change the properties of some
>>    characters, but also introduce additional embedding (or occasionally
>>    override) levels. Is this possible in your implementation?
>
>I'm not sure I understand: embeddings and overrides are fully
>supported, so what could be the problem?

Well, it's similar to character properties: What you definitely
support is the interpretation of RLE,... PDF characters to
create an embedding. But as explained, we don't actually want
to include these characters. As Kenichi explained, overlays
may be a way to get the characters to the display engine
without adding it to the text. Do you think this would
do the job?

Regards,    Martin.