This chapter was all about web forms and validating user input. There's a lot more to creating web forms than simply creating HTML controls, and here are some of the salient points in this chapter:
The special superglobal array, $_SERVER, contains a great deal of information about what's going on with your web application. $_SERVER['PHP_SELF'] holds the name of the current script, $_SERVER['REQUEST_METHOD'] holds the request method that was used ("GET", "POST", and so on), $_SERVER['HTTP_USER_AGENT'] holds the type of the user's browser, and so on. See Tables 6-1 and 6-2 for the details.
In web forms, you can redirect the browser with the header method like this: echo header("Location: new_url.html");.
You can combine web forms into one by checking if a user variable is set with the isset function; if so, data is waiting to be processed.
PHP provides a variety of ways to validate the data the user sent you, such as using regular expressions on text data.
To strip HTML tags, you can use the htmlentities function, which encodes HTML tags.