A source container or source image is an OCI artifact, that is an OCI
image with custom config (media type). There is a longer history behind
source images which are intended to ship the source artifacts of an
ordinary "executable" container image. Until now, source images at
Red Hat are built with github.com/containers/BuildSourceImage. We had a
growing desire (and always the long-term plan) to eventually replace
BuildSurceImage with something else, in this case Buildah.

PR: https://github.com/containers/buildah/pull/3101