+ appstream-util validate-relax --nonet /builddir/build/BUILDROOT/xfce4-screenshooter-1.8.2-1.fc22.x86_64//usr/share/appdata/xfce4-screenshooter.appdata.xml
/builddir/build/BUILDROOT/xfce4-screenshooter-1.8.2-1.fc22.x86_64//usr/share/appdata/xfce4-
FAILED:
? style-invalid         : <p> should not start with 'This application'
Validation of files failed

According to the spec... "Never start the first sentance with This application..." :) 

http://people.freedesktop.org/~hughsient/appdata/