DOCBOOK-APPS: HTML entities (XSL stylesheet 1.39)

Validating the generated HTML with a faq article, I get the following:

onsgmls -wmin-tag -s cygwin-xfree-faq.html
onsgmls:cygwin-xfree-faq.html:337:112:E: "X2018" is not a function name
onsgmls:cygwin-xfree-faq.html:340:40:E: "X2019" is not a function name
onsgmls:cygwin-xfree-faq.html:365:60:E: "X2018" is not a function name
onsgmls:cygwin-xfree-faq.html:365:274:E: "X2019" is not a function name

If I read the HTML 4.01 spec correctly, this is because html expects
‘
not
‘

As far as I can tell this is coming from the common/en.xml localisation
file (overriding dingbat.characters didn't fix it.
However, as en.xml covers more than just html, I was wondering about the
best approach to fix this?

Rob