$ appstream-util validate-relax gnome-gmail.appdata.xml.in
gnome-gmail.appdata.xml.in: FAILED:
• tag-invalid : <release> versions are not in order [2.0 before 2.0.1]
• tag-invalid : <release> versions are not in order [2.0.1 before 2.1]
• tag-invalid : <release> versions are not in order [2.1 before 2.2]
• tag-invalid : <release> versions are not in order [2.2 before 2.3]
• tag-invalid : <release> versions are not in order [2.3 before 2.3.1]
• tag-invalid : <release> timestamps are not in order [1450790604 before 1451180280]
• tag-invalid : <release> timestamps are not in order [1451180280 before 1464383933]
• tag-invalid : <release> timestamps are not in order [1464383933 before 1467166565]
• tag-invalid : <release> timestamps are not in order [1467166565 before 1483500463]
• tag-invalid : <release> timestamps are not in order [1483500463 before 1483845277]
Validation of files failed