docs: def add_missing_children(models,request,include_children_for,modelgb):
    "helper for do_check. mutates request"
    for (nombre,pkey),model in models.items():
      for modelclass,pkeys in model.refkeys(include_children_for.get(nombre,())).items():
        # warning: this is defaulting to all fields of child object. don't give clients a way to restrict that until there's a reason to.
        childname=modelgb['row',modelclass].name
        for childfield,cftype in modelclass.FIELDS:
          if not isinstance(cftype,basestring) and inspect.isclass(cftype) and issubclass(cftype,syncschema.Syncable):
            merge_null_missing(request,childname,childfield,pkeys)
          elif childfield in modelclass.SENDRAW: merge_null_missing(request,childname,childfield,pkeys)
          else: pass # intentional: ignore the field
    return request # the in-place updated original