These commands are not available from the branch popup by default.
This command shelves a branch. This is done by deleting the branch, and creating a new reference "refs/shelved/BRANCH-NAME" pointing at the same commit as the branch pointed at. If the deleted branch had a reflog, then that is preserved as the reflog of the new reference.
This is useful if you want to move a branch out of sight, but are not ready to completely discard it yet.
This command unshelves a branch that was previously shelved using
magit-branch-shelve. This is done by deleting the reference
"refs/shelved/BRANCH-NAME" and creating a branch "BRANCH-NAME"
pointing at the same commit as the deleted reference pointed at.
If the deleted reference had a reflog, then that is restored as
the reflog of the branch.