Regex engine
https://www.regular-expressions.info/engine.html
https://se.ifmo.ru/~ad/Documentation/Mastering_RegExp/mastregex2-CHP-4.html
https://devopedia.org/regex-engines
https://www.codeguru.com/cpp/cpp/cpp_mfc/parsing/article.php/c4093/Write-Your-Own-Regular-Expression-Parser.htm