The functions in this section do not fit neatly into any other section of the functional reference. They are not available by default when compiling PHP, and most of them require extra libraries. While none are essential to building PHP scripts, some are quite useful in the right context. Because you may not be familiar with all the technologies in this chapter, I've attempted to give a brief synopsis and links to Web sites where you can learn more.
The list of extensions is growing rapidly. A few didn't make it into this edition of the book for several reasons. Some are very specialized, and perhaps not of general interest. ...