update preg_match_all() example

git-svn-id: https://svn.php.net/repository/phpdoc/en/trunk@29413 c90b9560-bf6c-de11-be94-00142212c4b1

functions/pcre.xml

@@ -248,6 +248,9 @@ preg_match_all ("/\(?  (\d{3})?  \)?  (?(1)  [\-\s] ) \d{3}-\d{4}/x",
      <example>
       <title>Find matching HTML tags (greedy)</title>
       <programlisting role="php">
+// the \\2 is an example of backreferencing. This tells pcre that
+// it must match the 2nd set of parenthesis in the regular expression
+// itself, which would be the ([\w]+) in this case.
 $html = "&lt;b&gt;bold text&lt;/b&gt;&lt;a href=howdy.html&gt;click me&lt;/a&gt;
 
 preg_match_all ("/(&lt;([\w]+)[^&gt;]*&gt;)(.*)(&lt;\/\\2&gt;)/", $html, $matches);