I'm trying to recall the XML tool you said you use, but Oxygen has the real time xPath too per my image above.
Supported databases, like MySQL, SQL Server, Oracle and the like (but not FileMaker) also support SQL against the database to get the records you want first. Then, you can export them as XML, (or JSON) create an XSL schema, or whatever.
Thanks for your post.
I use xmplify (on Mac). I just checked and it does not have connect to source via xDBC. It does create the XSD for you if needed. It does transform (with XSLT) and you can specify several processors (LibXSLT is the default). The error checking is the best.
I also just code in BBEdit, because I can.
p.s. by-the-way, "FMPDSORESULT" grammar has been deprecated for years. It can still be used for Exporting XML, but the FMPXMLRESULT grammar is used for Import, so I only use that grammar.