SYNSEM.ATTACH constraints

Could anyone explain the purpose of these constraints:

;Constraint on MC used to be part of matrix.tdl
;;it applies to all wo implementations, except for v2

head-initial-head-nexus := head-initial &
  [ SYNSEM.ATTACH lmod,
    HEAD-DTR.SYNSEM.ATTACH notmod-or-lmod ].

head-final-head-nexus := head-final &
  [ SYNSEM.ATTACH rmod ].

I think it’s about keeping a lid on ambiguity when you have a head-medial construction where things can attach both left & right and there’s nothing else blocking ambiguity about which attaches first. Probably from @antske’s work on V2 order.