/usr/include/muffin/meta/ is in libmuffin-dev 2.2.6-4.
This file is owned by root:root, with mode 0o755.
..
/usr/include/muffin/meta/atomnames.h
/usr/include/muffin/meta/boxes.h
/usr/include/muffin/meta/common.h
/usr/include/muffin/meta/compositor-muffin.h
/usr/include/muffin/meta/compositor.h
/usr/include/muffin/meta/display.h
/usr/include/muffin/meta/errors.h
/usr/include/muffin/meta/gradient.h
/usr/include/muffin/meta/group.h
/usr/include/muffin/meta/keybindings.h
/usr/include/muffin/meta/main.h
/usr/include/muffin/meta/meta-background-actor.h
/usr/include/muffin/meta/meta-plugin.h
/usr/include/muffin/meta/meta-shadow-factory.h
/usr/include/muffin/meta/meta-shaped-texture.h
/usr/include/muffin/meta/meta-window-actor.h
/usr/include/muffin/meta/prefs.h
/usr/include/muffin/meta/preview-widget.h
/usr/include/muffin/meta/screen.h
/usr/include/muffin/meta/theme.h
/usr/include/muffin/meta/types.h
/usr/include/muffin/meta/util.h
/usr/include/muffin/meta/window.h
/usr/include/muffin/meta/workspace.h