Fun With Schemas

This one is fun.  I know that a validating editor 
can use a schema or DTD to create a valid file.  

Can a program do this for files it creates dynamically?
Are there examples of this?

This question came from a programmer who doesn't want 
to hardwire the structure of files she creates into 
the code that creates them.  I had replied with validation 
on input (create the file, validate it then), and what 
she actually wants to do is use the schema to drive 
the file builder using say, SAX or its analog.  Mainly, 
she doesn't want to rewrite the code when new versions 
of the document inevitably occurs.  She just wants to 
modify the schema.  Works for editors but of course, 
they run in human time, but other than performance, I 
can't think of a reason WHY she couldn't do it.

What about it?

len