/usr/share/SuperCollider/Extensions/ is in supercollider-emacs 1:3.7.0~repack-4+deb9u1.
This file is owned by root:root, with mode 0o755.
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/usr/share/SuperCollider/Extensions/scide_scel/
/usr/share/SuperCollider/Extensions/scide_scel/Document.sc
/usr/share/SuperCollider/Extensions/scide_scel/Emacs.sc
/usr/share/SuperCollider/Extensions/scide_scel/EmacsBuffer.sc
/usr/share/SuperCollider/Extensions/scide_scel/EmacsDocument.sc
/usr/share/SuperCollider/Extensions/scide_scel/ScelDocument.sc
/usr/share/SuperCollider/Extensions/scide_scel/extBuffer.sc
/usr/share/SuperCollider/Extensions/scide_scel/extClassBrowser.sc
/usr/share/SuperCollider/Extensions/scide_scel/extString.sc
/usr/share/SuperCollider/Extensions/scide_scel/homeContext.sc
/usr/share/SuperCollider/Extensions/scide_scel/storeLispOn.sc