lib/proto.js
function subRegister(obj, name) {
  var res;
  res = isPrimitive(obj[name]) ? {} : obj[name];
  return obj[name] = mixable(res).mixin(proto, 'register', 'extend');
}
function subRegister(obj, name) {
  var res;
  res = isPrimitive(obj[name]) ? {} : obj[name];
  return obj[name] = mixable(res).mixin(proto, 'register', 'extend');
}
Get or build a sub register for an object.