An excellent and very useful addition to PCRE is the concept of named capturing groups (which everybody always refers to as named patterns). A named capturing group lets you refer to a subpattern of your expression by an arbitrary name, rather than by its position inside the regular expression. For example, consider the following regex:
/^Name=(.+)$/
Now, you would normally address the (.+) subpattern as the first item of the match array returned by preg_match() (or as $1 in a substitution performed through a call to preg_replace() or preg_replace_all()).
That's all well and goodat least as long as you have only a limited number of subpatterns whose position never changes. Heaven forbid, however, that you should ever find yourself in a position to have to add a capturing subpattern at the beginning of a regex that already has six of them!
Luckily, this problem can be solved once and for all by assigning a "name" to each of your subpatterns. Take a look at the following:
/^Name=(?P<thename>.+)$/
This will create a backreference inside your expression that can be explicitly retrieved by using the name thename. If you run this regex through preg_match(), the backreference will be inserted in the match array both by number (using the normal numbering rules) and by name. If, on the other hand, you run it through preg_replace(), you can backreference it by enclosing it in parentheses and prefixing it with ?P=. For example:
preg_replace ("/^Name=(?P<thename>.+)$/", "My name is (?P=thename)", $value); you may want to include an example of this functionality.
