Gentoo's portage package manager uses configuration files to unmask unstable branch packages to install, configure package-specific USE flags or choose which software licenses to accept. The emerge command can automatically add entries to these files when they are required. These entries look like this:
# required by media-sound/ardour-3.5.403::gentoo[lv2]
# required by @selected
# required by @world (argument)
=dev-libs/serd-0.20.0 ~amd64
# required by media-sound/ardour-3.5.403::gentoo[lv2]
# required by @selected
# required by @world (argument)
=dev-libs/sord-0.12.2 ~amd64
This utility sorts configuration files by package atom keeping the comment blocks above the relevant entries. Multiple keywords/flags/licenses on each line are also sorted keeping the package atom at the start of the line.