# Regex to find invalid characters in filter or actions **URL:** https://community.mp3tag.de/t/regex-to-find-invalid-characters-in-filter-or-actions/17008 **Category:** Support **Created:** [June 30, 2015, 1:49pm UTC](https://community.mp3tag.de/t/regex-to-find-invalid-characters-in-filter-or-actions/17008 "2015-06-30T13:49:58Z") **Posts on this page:** 1 **Showing post:** 9
### Author: ![DetlevD](https://community.mp3tag.de/user_avatar/community.mp3tag.de/detlevd/32/123_2.png) [@DetlevD](https://community.mp3tag.de/u/DetlevD) #### Post date: [July 2, 2015, 11:51am UTC](https://community.mp3tag.de/t/regex-to-find-invalid-characters-in-filter-or-actions/17008/9 "2015-07-02T11:51:13Z")
> [@111MilesToGo](#): > > Now that we agree that there is something strange regarding the MATCHES operator in file list filter expressions, I think it is the time now for Florian Heidenreich (or his coworkers if any) to step in and clarify this matter. ... Yes. > [@111MilesToGo](#): > > ... To DetlevD (we could also talk German, of course ...): Thanks for your testing and agreeing with me, as well as for your pointing me to the Boost C++ library. Are you implying that Mp3tag is using this library, which provides for Perl and POSIX (extended and more) regex handling? ... In the "About" dialog of older versions of Mp3tag application there was a human readable note about the implemented "boost" regex machine. Even in the code of the last version 2.70 of Mp3tag.exe one can find text from the boost "regex\_constants.hpp". I am still convinced that Mp3tag uses the boost regex machine. See also .... [Replace with Regular Expression](https://community.mp3tag.de/t/8140/3) [Capitalizing names with Mc/Mac](https://community.mp3tag.de/t/13838/5) [Expression to delete defined strings from tag](https://community.mp3tag.de/t/15409/22) DD.20150702.1556.CEST --- _[View the full topic](https://community.mp3tag.de/t/regex-to-find-invalid-characters-in-filter-or-actions/17008)._