I'm looking for an XML instance editor that validates against XML Schemas so
that the user doesn't create invalid documents and uses the schema to build
the interface, for things that are choices, and supports ensuring referential
integrity for keyref statements.  I'd preferably like something that's open
source and runs on Linux, but the target platform is Windows and if need be,
it can be commercial.  Any ideas?

-- 
Jon Schewe | http://mtu.net/~jpschewe | jpschewe at mtu.net
For I am convinced that neither death nor life, neither angels 
nor demons, neither the present nor the future, nor any 
powers, neither height nor depth, nor anything else in all 
creation, will be able to separate us from the love of God that 
is in Christ Jesus our Lord. - Romans 8:38-39