[XeTeX] strande behavior of Linux Libertine fonts with optio Fractions=On

[mskala at ansuz.sooke.bc.ca]

On Thu, 13 Jan 2011, François Patte wrote:
> Who can explain (and correct if possible) this strange behaviour of the
> Linux Libertine fonts if you add the option "Fractions=On"
>
> If you put a number with more than one digit,  only the last number has
> the normal size, the preceding digits are written like exponants before it.

You should only turn the fractions option on where you actually want
a fraction; it assumes that all sequences of digits will be parts of
fractions and attempts to translate them appropriately.  Leaving it on for
general text will result in non-fraction digit sequences being messed up,
as you've discovered.

The reason it can't detect the presence of a slash, and only translate
digits when the slash is present, is because glyph substitution rules
can't do arbitrary-length look-ahead.  When it sees the first digits of
the numerator it has to make a decision on whether to raise them, even
before it sees the slash.  This posting on my Web log gives some technical
details of how such features are implemented, which may be illuminating:

   http://ansuz.sooke.bc.ca/entry/131

> Suppress the option "Fractions=On" and everything is OK...

That's what you have to do, unfortunately: you can't both have automatic
translation of arbitrary-length fractions, and leave digit sequences
without a slash intact.
-- 
Matthew Skala
mskala at ansuz.sooke.bc.ca                 People before principles.
http://ansuz.sooke.bc.ca/