vector<Box> head_extents;
for (vsize i = heads_and_stems.size (); i--;)
head_extents.push_back (Box (heads_and_stems[i]->extent (common[X_AXIS], X_AXIS),
vector<Box> head_extents;
for (vsize i = heads_and_stems.size (); i--;)
head_extents.push_back (Box (heads_and_stems[i]->extent (common[X_AXIS], X_AXIS),