Why is PHP_EOL in PHP ineffective?

Why is PHP_EOL in PHP ineffective? The following procedure:

 Error code :['. $ errno. ']'. $ errstr. PHP_EOL; echo 'line of code where the error is located :'. $ errline. 'file '. $ errfile. PHP_EOL; echo 'php version :'. PHP_VERSION. '('. PHP_ OS. ')'. PHP_EOL; die ();} set_error_handler ('customerror', E_ALL | E_STRICT); $ a = array ('O' => 2, 4, 6, 8 ); echo $ a [o];

Output:
Error code: [8] Use of undefined constant o-assumed 'O' the error code line: 12 file/usr/local/apache/htdocs/mytest/test2.php PHP version: 5.4.19 (Linux)

There is no line feed in the middle. why ??

My environment is centos

Reply to discussion (solution)

Echo $ a ['O'];

Line Feed is

PHP_EOL is text wrap, not html wrap

Thank you!