Warning: include(external_file.php): Failed to open stream: No such file or directory in /home/course/u90/public_html/examples_php_annotated/core/error5.php on line 11

Warning: include(): Failed opening 'external_file.php' for inclusion (include_path='.:/usr/share/php') in /home/course/u90/public_html/examples_php_annotated/core/error5.php on line 11
The preceding code in this script tried to include a file
that does not exist, and so generated a "warning error",
but the script carries on and outputs the text you are reading.