We introduce a relation on real conjugacy classes of SL(2)-orbits in a
Mumford-Tate domain D which is compatible with natural partial orders on the
sets of nilpotent orbits in the corresponding Lie algebra and boundary orbits
in the compact dual. A generalization of the SL(2)-orbit theorem to such
domains leads to an algorithm for computing this relation, which is worked out
in several examples and special cases including period domains, Hermitian
symmetric domains, and complete flag domains, and used to define a poset of
equivalence classes of multivariable nilpotent orbits on D.