can some explain this : (?<!<)

[PHP-ing]

can anyone explain this part of codes? TY.I need to do documentation for my codes. But i dun seem to know what the following does : \b(?<!<)

if(strtoupper($searchword ) == 'b')
   {
    $trimmed_arrayKeyword[$trimmKeyword] = "/\b(?<!<)$searchword(?!<)\b/i";
    continue;
   }

else $trimmed_arrayKeyword[$trimmKeyword] = '/\b('.preg_quote($searchword,'/').')\b/i';

[drew010]

its a regular expression. \b denotes a word boundary (start or end of a string), the ?<! followed by the < says to look for $searchword as long as it isnt preceded by a <, and the ?! followed by < says the thing after search word should not be a <.

see http://php.net/manual/en/reference.pcre.pattern.syntax.php for more info