I think we can do this already, using \XeTeXinterchartoks (see XeTeX-reference.pdf) - just set it up so that whenever the string "ra" appears, the appropriate kern is inserted automatically, etc. I don't know if it is possible to get this working for italic text only, unless you redefine \itshape, but I wouldn't recommend that unless you know exactly what you are doing (or someone else can do it for you).<br>
<br>Andrew<br><br><br><div class="gmail_quote">2009/10/7 John Was <span dir="ltr"><<a href="mailto:john.was@ntlworld.com">john.was@ntlworld.com</a>></span><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div bgcolor="#ffffff">
<div><font face="Arial Unicode MS" size="2">Hello</font></div>
<div><font face="Arial Unicode MS" size="2"></font> </div>
<div><font face="Arial Unicode MS" size="2">I expect it's too late for the
official 2009 TeXLive, but I thought I'd reiterate my request for some facility
to tweak the kerning pairs in any given font by an external command - at font
loading this would be something like 'kering=mykerns', </font><font face="Arial Unicode MS" size="2">analogous to 'mapping=tex-text', the 'mykerns' file
being something that users could compile for themselves according to a specified
syntax.</font></div>
<div><font face="Arial Unicode MS" size="2"></font> </div>
<div><font face="Arial Unicode MS" size="2">The issue has come up again recently
when I moved over to the Open Type version of Monotype's Imprint font (Imprint
Pro) for continuity of appearance in a periodical as I changed over from an old
EmTeX system to XeTeX: disappointingly, the italic font continues to give
bad spacing between lower-case 'r' and some following letters, most noticeably
'a', which is a nuisance as there is often citation of books
with words like 'morality', 'fragility' in the title. The flaw always
did exist in the font since digitization, but it seems that
the manufacturer hasn't made any improvements to the kerning.
Until they do (it could be a long wait), it would be most convenient just to
specify some space between 'r' and 'a' (etc.), to avoid workarounds such as
'r\kern 1sp a', which of course breaks the hyphenation algorithm as well as
cluttering up the file.</font></div>
<div><font face="Arial Unicode MS" size="2"></font> </div>
<div><font face="Arial Unicode MS" size="2">I seem to recall that when it was
discussed before, others said it would be useful, so I'm just trying to make
sure it eventually moves from 'pending' to 'active' rather than
'ditched'...</font></div>
<div><font face="Arial Unicode MS" size="2"></font> </div>
<div><font face="Arial Unicode MS" size="2">Best</font></div>
<div><font face="Arial Unicode MS" size="2"></font> </div>
<div><font face="Arial Unicode MS" size="2"></font> </div>
<div><font face="Arial Unicode MS" size="2">John</font></div>
<div><font face="Arial Unicode MS" size="2"></font> </div></div>
</blockquote></div><br>