This chapter introduced regular expressions, including the various different ways in which they are implemented in PHP5. You learned how to write these using the POSIX regular expression syntax, including creating multi-byte aware expressions. Using these, we then showed how to perform common data-validation tasks with minimal code, letting the regular expression processors do most of the complicated work. This chapter also examined a few other functions that use regular expressions.
We next move on to some other features we will commonly use or encounter as we write web applications. The first of these are XML and XHTML, the latter of which we will use to generate the user interface for our applications.