Method $zip->UnzipMatching($dirPath, $pattern, $verbose);
$pattern should be a Regular Expression. That way you can set Beginning with, ending with, OR patterns, much more.
I'm sorry to say that the pattern is only a wildcarded pattern, where "*" represents 0 or more of any char. Chilkat does not use regular expressions because of the cross-platform / cross-language requirements, and unless Chilkat implemented regular expressions directly, it would need to rely on whatever was available in each environment, which would lead to dependencies, complications, differences between platforms, etc..