Post #1902084

@joe9nf @craftyguy """ When one or more system extension images are activated, their /usr/ and /opt/ hierarchies are combined via "overlayfs" with the same hierarchies of the host OS, and the host /usr/ and /opt/ overmounted with it ("merging"). """ https://www.freedesktop.org/software/systemd/man/latest/systemd-sysext.html