This post is optional and can be used by those students that want to go beyond the regular content of the course. Files is an optional topic here because we are trying to get to the really powerful technology that will dramatically increase the value of everything you've learned so far - online databases.
The video discusses the use of the array of $_SERVER variables as a source of information that is possible to obtain in communications with the server in addition to the information stored in PHP variables and in files/databases in various locations. Then we will briefly touch on the basics of the file operations and the need to open and close them before and after processing.
Then you will see a couple of simple applications that can be creatively modified, and even serve as a basis of a start-up company or a very useful addition to your project site. In this applications we will use Ajax to create the connection to the server and PHP for processing on the server side.
