According to codesearch, this is the only place the XS field is used in Debian: https://codesearch.debian.net/results/%20path%3Adebian%2Fcontrol%20XS-Build-Indep-Architecture
and therefore triggers https://lintian.debian.org/tags/unknown-field-in-dsc.html piuparts complains too: https://piuparts.debian.org/sid/source/p/pixfrogger.html Thanks, Jeremy Bicha
