Hi Trevor,
There is no default XML application setting in frame (never has been to my knowledge).
When frame opens XML instance, the only thing it looks is the root element name. This is compared to DOCTYPE values in structapps file.
If only one application match is found, XML gets parsed (the public declarations in application are passed to xerces instead of normal catalog support) and fed to frame through corresponding rw-rules.
If more than one doctype matches, frame asks which application to use.
Nasty feature..especially in applications using same dtd/schema and needing multiple page sizes..frame keeps asking application all the time.
During XML write, the writer rule does the same thing..writing public identifier (and system, too), otherwise the external parser would not be able to resolve the dtd/schema location.
BR, Martti