/etc/blends/sources.list.UNRELEASED is in blends-dev 0.6.16.4ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 | # For testing purposes this sources.list might be useful. It is a
# good practice to use UNRELEASED in the changelog as target distribution
# for not yet finished packages and blends-dev should also work in this
# case
deb http://ftp.debian.org/debian unstable main
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