setfacl
AccountsPackage: acl
Adds rights to a file that the usual nine characters cannot express: one specific account for reading, one more group for writing. ls -l then shows only a +; the rest is read with getfacl.
What its options do in the lessons
From the same glossary the lessons render under their commands, so the two cannot disagree.
setfacl -m- Adds or modifies one entry in the list:
u:carol:rXgrants that single account read, plus traversal when the entry targets a directory — without touching the owner, the group or others.
Lessons that teach it
No lesson names it among its useful commands; it appears inside other lessons' command lines.