When a witness gives information about something that she did not see herself and she only knows that thing because someone else told her about it or because someone else wrote about it.
Error message
Deprecated function: rtrim(): Passing null to parameter #1 ($string) of type string is deprecated in Drupal\advagg_mod\EventSubscriber\InitSubscriber->onEvent() (line 130 of modules/contrib/advagg/advagg_mod/src/EventSubscriber/InitSubscriber.php).
Drupal\advagg_mod\EventSubscriber\InitSubscriber->onEvent(Object, 'kernel.request', Object) call_user_func(Array, Object, 'kernel.request', Object) (Line: 142) Drupal\Component\EventDispatcher\ContainerAwareEventDispatcher->dispatch(Object, 'kernel.request') (Line: 145) Symfony\Component\HttpKernel\HttpKernel->handleRaw(Object, 1) (Line: 81) Symfony\Component\HttpKernel\HttpKernel->handle(Object, 1, 1) (Line: 58) Drupal\Core\StackMiddleware\Session->handle(Object, 1, 1) (Line: 48) Drupal\Core\StackMiddleware\KernelPreHandle->handle(Object, 1, 1) (Line: 191) Drupal\page_cache\StackMiddleware\PageCache->fetch(Object, 1, 1) (Line: 128) Drupal\page_cache\StackMiddleware\PageCache->lookup(Object, 1, 1) (Line: 82) Drupal\page_cache\StackMiddleware\PageCache->handle(Object, 1, 1) (Line: 48) Drupal\Core\StackMiddleware\ReverseProxyMiddleware->handle(Object, 1, 1) (Line: 51) Drupal\Core\StackMiddleware\NegotiationMiddleware->handle(Object, 1, 1) (Line: 23) Stack\StackedHttpKernel->handle(Object, 1, 1) (Line: 718) Drupal\Core\DrupalKernel->handle(Object) (Line: 19)