For each PDF/A-1 validation issue we try to explain what it means and, if possible how to resolve it. For a more technical explanation of the issue we quote the related section of the ISO 19005-1 PDF/A Specification.
All content of all XMP packets shall be well-formed as defined by Extensible Markup Language (XML) 1.0 (Third Edition), 2.1, and RDF/XML Syntax Specification (Revised), 7. If possible, at the time a writer creates or resaves a conforming file all of the content of that file's XMP packets should be validated.