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Chapter 14 PCRE Extension There are some instances where markup documents may be so hideously malformed that they’re simply not usable by an XML extension. Other times, you may want to have a way to check the data you’ve extracted to ensure that it’s what you expect. Changes to the structure of markup documents may be significant, to the point where your CSS or XPath queries return no results. They may also be small and subtle, such that while you do get query results, they contain less or different data than intended. While either of these tasks could be done with basic string handling functions and comparison operators, in most cases the implementation would prove to be messy and unreliable. Regular expressions provide a syntax consisting of meta-characters whereby patterns within strings are expressed flexibly and concisely. This chapter will deal with regular expressions as they relate to the P e r l - C o m p a t i b l e Regular Expression (PCRE) PHP extension in particular. A common bad practice is to use only regular expressions to extract data from markup documents. While this may work for simple scripts that are only intended to be used once or very few times in a short time period, it is more difficult to maintain and less reliable in the long term. Regular expressions simply were not designed for this purpose, whereas other markup-specific extensions discussed in previous chapters are more suited for the task. It is a matter of using the best tool for the job, and to that end, this practice should be avoided.
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vi ” CONTENTS Referring URLs . .
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Chapter 1 Introduction If you are l
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Introduction ” 3 in some instance
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