toXML method
Implementation
String toXML() {
return '''<printDocument documentID="$documentID" stockName="$stockName">
${pdfs.isEmpty?'': pdfs.map((e) => '''<pdfPrintDocument>$e</pdfPrintDocument>\n''').join()}
${textDocuments.isEmpty?'': ''''<simpleTextPrintDocument>${textDocuments.map((e) => e.toXML()).join()}</simpleTextPrintDocument>'''}
</printDocument>
''';
}