However you can use the numeric Unicode values directly
... ouml ... #246 ... ö
We deliberately did not define a DTD for the site.xml so leaving it to be able to use any element names. Hence we did not include the usual collections of named character entities.
You can explicitly declare these in an internal DTD subset for your local version of site.xml ...
<!DOCTYPE site [
<!ENTITY % ISOlat1 PUBLIC
"ISO 8879:1986//ENTITIES Added Latin 1//EN//XML"