> The saving grace is that there's usually nothing to prevent a 
> version 2 
> implementation from also providing the methods required by version 3, 
> even though it isn't required to in a version 2 system. In this case, 
> the Saxon classes could add the extra methods required by DOM Level 3 
> because the DOM Level 2 methods are a minimal set, not a maximal set.

It's not quite so easy. One of the new methods in DOM3 is
getSchemaTypeInfo(), which returns an object of type TypeInfo, and TypeInfo
is an interface that's not available in JDK 1.4. So to produce an
implementation that compiles under JDK 1.5, I need to declare a method that
returns a TypeInfo, and this method won't compile under JDK 1.4 because
TypeInfo is not present. Currently, I don't see a way around this. It might
be possible to get round it by issuing dummy versions of the JDK 1.5
interfaces, but it's certainly very fiddly.

At present I'm a little inclined to take an axe to the problem, and stop
implementing DOM interfaces in the Saxon tree model. Instead I could provide
a DOM wrapper around the Saxon tree model. That would then be an optional
component that people could leave out if it causes configuration problems.

Michael Kay