Well- formed XML documents have sufficient structure to. Validate XML documents against their XSD schemas. Open the XML validation results panel by going to Packages - > XML Validate - > Toggle. xmllint - - noout your_ test_ file. Check for return code of this command. See documentation. up vote 2 down vote. xmllint - - valid - - encode utf- 8 TEST. will validate and output TEST. xml in utf- 8 cat TEST. < xml version= " 1. 0" encoding= " utf- 8"?