[XeTeX] Roman Numerals as stylistic alternatives

[Ross Moore]

Hello Enrico,

On 20/06/2011, at 5:42 AM, enrico.gregorio at univr.it wrote:

> What the OP wants is that "CXV" is stored as a unique glyph representing 115.
> Maybe this can be done by reserving, say, five thousand slots in Unicode to
> contain the numbers from 1 to 5000 in Roman form that are built from the basic
> digits, embedding in the font (or in the typesetting engine) the algorithm for building
> them from the Western/Arabic representation.

No.
In the PDF ISO standard, you have the option of using /ActualText tagging.
The PDF would contain a portion of the page contents stream, such as:

  /Span<</ActualText(115)>>BMC .... (graphics to position and produce 
the letters 'C' 'X' and 'V' ) ... EMC

Now *any* attempt to select any portion of the visible string "CXV"
is supposed to result in the whole string being included when copying.

The problem is that not all PDF browsers are fully conformant, so this
behaviour may not be what you actually get with a particular piece of
software.  (BTW, Apple is one of the biggest offenders.)

> This might be done in two passes:
> represent the number using the codes for Roman numerals and start a ligaturing
> process.

Trying to do it character by character at the font level doesn't seem
overly practical to me. The concept is the number "123" but represented
in a non-standard way. The use of /ActualText tagging seems to be much
more helpful to readers, and also to other software that tries to
extract the meaning being represented with a PDF, for whatever purpose.

Note that ISO PDF also has an alternative method of tagging.
E.g.
    /Span<</Alt(123)>>BMC .... EMC
Screen-readng software is meant to use the /Alt tagging.

And both /Alt and /ActualText allow multiple values having been preceded
by a /Lang tag, so that the actual vocalization generated by the 
screen-reader can be adjusted for different languages --- the document 
author normally would provide this, but a sophisticated PDF browser 
plug-in might be programmed to produce a translation on-the-fly.

> 
> Actually, Roman numerals are mostly used when the numerical information is
> almost irrelevant as such. Nobody uses the "XIV" in "Louis XIV" to perform
> calculations. That's just a different way of writing "quatorze". 

Right. So /ActualText tagging can support this distinction in meaning.
It is *not* intended to support calculations --- that is the domain
of "Content Tagging" using MathML.

> 
> I see it just as the ability to copy "quatorze" from a text and paste it into a
> worksheet cell accepting numbers to get 14. In the case of Roman numerals
> it may be simpler, of course. But is it useful?

Most certainly it is useful.
It is part of the way of the future for smart PDF documents.


> 
> Ciao
> Enrico


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Ross Moore                                       ross.moore at mq.edu.au 
Mathematics Department                           office: E7A-419      
Macquarie University                             tel: +61 (0)2 9850 8955
Sydney, Australia  2109                          fax: +61 (0)2 9850 8114
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