[xml] Schema creation - hints, tips, tricks, tools?

[David Hagood <wowbagger sktc net>]

Does anybody have any good trick, tips, tools or advice on creating a good
schema for a given XML grammer?

Ideally, I'd like something that, given a file that is supposed to be
valid, would spit out a schema as a starting point - it usually being
easier to edit an existing file than to start from scratch.

Obviously, there is no way to go from an example to a schema with 100%
success - things the example does not contain cannot be inferred.

But as a way to get started, it would be a leg up.

Are there any good schema creation/editing tools I should look at?