$ curl --silent --show-error --location --output nextcloud_rss.xml https://nextcloud.com/blogfeed
$ xmllint --noout nextcloud_rss.xml 
nextcloud_rss.xml:1: parser error : XML declaration allowed only at the start of the document
sAf_qakmgr7JkZB62coshuOa3J_psCRc7RiZK5s6ByrnvHvZQoFsxc.css" media="all" /> <?xml
                                                                               ^
nextcloud_rss.xml:1: parser error : Extra content at the end of the document
iZK5s6ByrnvHvZQoFsxc.css" media="all" /> <?xml version="1.0" encoding="UTF-8"?> 
                                                                               ^
$