https://www.markdownguide.org/extended-syntax/
Extended Syntax | Markdown Guide
Advanced features that build on the basic Markdown syntax.
extended syntaxmarkdown guide
https://www.boost.org/doc/libs/1_47_0/libs/regex/doc/html/boost_regex/format/boost_format_syntax.html
Boost-Extended Format String Syntax
format stringboostextendedsyntax