Did you ever want to run MSXML or Saxonica (Saxon-SA) as XML validator directly in XMLSpy? Without starting a batch file, maybe copy-pasting the path of the current document and looking at the results in a DOS box?
If so, ValidatorBuddy will be your friend.
Check your XML files with the most popular validators available. Compare the different Validator outputs to get more informations about errors in your XML. See the results directly in XMLSpy and fix any validation errors. The Error Output window is fully editable and you can Copy-Paste the validation results.