assert_is_mts(x, severity = getOption("assertive.severity", "stop"))
assert_is_ts(x, severity = getOption("assertive.severity", "stop"))
assert_is_tskernel(x, severity = getOption("assertive.severity", "stop"))
is_mts(x, .xname = get_name_in_parent(x))
is_ts(x, .xname = get_name_in_parent(x))
is_tskernel(x, .xname = get_name_in_parent(x))