XML::Checker ERROR-101: undefined ELEMENT [series]
        Context: line 2, column 0, byte 40
XML::Checker ERROR-101: undefined ELEMENT [article]
        Context: line 3, column 6, byte 56
XML::Checker ERROR-101: undefined ELEMENT [url]
        Context: line 4, column 13, byte 80
XML::Checker ERROR-101: undefined ELEMENT [title]
        Context: line 5, column 13, byte 167
XML::Checker ERROR-101: undefined ELEMENT [summary]
        Context: line 6, column 13, byte 239
data.xml passed validation