texmath-0.9.4: tests/writers/msubsup-04.eqn
A sub {C sub 4 sup 3} sup {B sub 2 sup 1} = A sub {C sub {4 sub {hphantom {roman "l"}}} sup 3} sup {B sub 2 sup {1 sup {hphantom {roman "s"}}}}
A sub {C sub 4 sup 3} sup {B sub 2 sup 1} = A sub {C sub {4 sub {hphantom {roman "l"}}} sup 3} sup {B sub 2 sup {1 sup {hphantom {roman "s"}}}}