PLEASE NOTE!!!! Since this video was made, info465.us has been secured with ssl. The error log is now /var/log/httpd/ssl_error_log, it is no longer at /var/log/httpd/error_log.
When you see the Refreshed source code is the current version with your changes, go back to the web page and refresh it.
This aggressive cacheing also complicates debugging CSS and it can be explicitly refreshed the same way.
If an SQL statement embedded in PHP code is not getting the expected results it's helpful to echo the statement to the browser so you can copy the _exact_ statement and paste it into the MySQL/MariaDB command line to see the error messages MySQL produces. When debugging the PHP script, the only thing you know is that the statement didn't work. Pasting the statement into the database's command line and running it there usually points out the error so it can be fixed.