promql/lex.go
func (i ItemType) isSetOperator() bool {
	switch i {
	case ItemLAND, ItemLOR, ItemLUnless:
		return true
	}
	return false
}
func (i ItemType) isSetOperator() bool {
	switch i {
	case ItemLAND, ItemLOR, ItemLUnless:
		return true
	}
	return false
}
// isSetOperator returns whether the item corresponds to a set operator.