Joe Sylve 
Volume grafting mounts a disk image's APFS contents as a subdirectory of an existing volume. This is the mechanism behind Cryptexes, RSRs, and system extensions.
New post on the lifecycle, constraints, and on-disk metadata:
Volume Grafting
Volume grafting is a mechanism introduced in macOS 13 that mounts a disk image’s APFS contents as a subdirectory of an existing volume. This is the technology behind Cryptexes, the cryptographically sealed, graftable disk images used for Rapid Security Responses and system extensions. This post covers the graft lifecycle, constraints, and on-disk metadata.
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