From recent replies, it seems that clicking on create/edit regex-function should reveal the code for built-in functions. My installation (Calibre 4.19 64-bit on Microsoft Windows [Version 10.0.18363.900]) does not.

Any ideas why? Have I turned something off inadvertently? Have I failed to install some module? Should I still be using OS/2?

Having some functions (more than what's in the manual) to play with will help me learn enough to fix my epub book library.

Any help you can give me (samples of code and search strings) will be greatly appreciated.