code: func ContainsLogIn(it Iterator, val Value) {
  	if clog.V(4) {
  		clog.Infof("%s %d CHECK CONTAINS %v", strings.ToUpper(it.Type().String()), it.UID(), val)
  	}
  }
docs: // Utility logging functions for when an iterator gets called Next upon, or Contains upon, as
  // well as what they return. Highly useful for tracing the execution path of a query.