RCREWS  Based on your feedback, version 1.4.1 appends a log to the report showing how many files it checked. I'm guessing you dragged a folder that did not contain any files with the recognized XML extensions. The version you reviewed shows a blank screen in this case. The readme describes how to add extensions to Validator's list of XML file name extensions. Thanks.  
(Version 1.4.1)

RCREWS  Thanks for the feedback. Validator is written to easily test multiple files at once. Drag the folder containing your Web site to the icon and Validator will evaluate all the XML on your site: XHTML, XSL, SVG, etc. Check out the readme for the details of what it tests, how it tests, and how it reports errors.  
(Version 1.4.1)