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Ligatures and caret position

From: Robin Berjon <robin.berjon@expway.fr>
Date: Wed, 2 Nov 2005 15:35:04 +0100
Message-Id: <34BE9131-619D-4752-AAF9-3D880DC8AF22@expway.fr>
Cc: SVG WG <w3c-svg-wg@w3.org>
To: public-i18n-core@w3.org

Dear I18N Core WG,

I am writing to you on behalf of the SVG WG. We have added support  
for editable text to the SVG Tiny 1.2 specification, which entails  
that during edition, a caret would typically be available (in visual  
media) for the user to know the current editing position in the text.  
Since we also support ligatures (including in SVG fonts), we were  
wondering how the caret should interact with them.

Let's assume that the user is editing the word "donkey", and that the  
"nke" characters were ligatured so as to render as an "X", giving us  
"doXy".

The user has the caret after the "o", like so: do|Xy. If she moves  
the caret one step further (in this case, to the right), what should  
happen? We can see several options:

  - the caret moves straight to after the glyph: doX|y. This is  
unintuitive for, say, an "fi" ligature, but may be the best option  
for some scripts.
  - same as the above, but script/language dependent so that it's  
(almost) always intuitive.
  - the caret doesn't move until it has been advanced (say, using the  
right arrow key) as many times as there are characters in the  
ligature. For instance, if the caret would conceptually be on "don| 
key" or "donk|ey" the rendering would still be "do|Xy". We believe  
that this is not a very intuitive option.
  - each time the caret is advanced, it progresses by the advance of  
the ligature glyph divided by the number of characters. This has the  
advantage that the user gets feedback for her actions, but we suspect  
that the result may be completely wrong in some situations.
  - we leave it completely up to implementations, hoping they'll get  
it right.

Note that everywhere in the above that concerns itself with advancing  
the caret would be expected to work conversely when it is moving  
backwards as well.

We would greatly appreciate your guidance in this issue. Thanks!

-- 
Robin Berjon
    Senior Research Scientist
    Expway, http://expway.com/
Received on Wednesday, 2 November 2005 14:35:07 GMT

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