Tests/feaLib/data/variable_mark_anchor.fea

markClass macron <anchor 0 (wght=200:150 wght=900:152)> @MC_top;

lookup one {
 pos base a
 <anchor 0 0> mark @MC_top;
} one;
lookup two {
  pos base a
  <anchor 0 0> mark @MC_top;
} two;