This page: https://help.libreoffice.org/latest/en-US/text/shared/01/02100001.html?&DbPAR=SHARED&System=UNIX is entitled "List of Regular Expressions". As you can imagine, it is not some arbitrary list of regular expressions - it describes, or specifies, the syntax of regular expressions usable in LibreOffice (Find and) Replace dialogs. So, I suggest improving the title. My suggestion: "Regular Expression syntax". (Unless someone has a better idea.)