v='*.z'
[[ a.z = *.z ]]; echo 1:YES:$?
[[ a.z = "*".z ]]; echo 2:no:$?
[[ a.z == $v ]]; echo 3:YES:$?

# Buggy:
# the problem is that expansion rules of LHS and RHS of ~=
# should not be the same: in RHS, "$v" and "*" should escape metas
# (currently "$v" does not),
# but in LHS, they should _not_ do that
# (currently "*" does). Thus these cases fail:
#[[ a.z == "$v" ]]; echo 4:no:$?	# BUG: "$v" expands to *.z
#[[ "*".z == ?.z ]]; echo 5:YES:$?	# BUG: "*" expands to \*