I don't think redcarpet is responsible for the markdown - it's simply a renderer; it uses some libraries to interpret the required code
After some research, it seems all of the markdown
interpreters are originally based on the UpSkirt
library, which was derived from this Daring Fireball project:
Markdown is a text-to-HTML conversion tool for web writers. Markdown
allows you to write using an easy-to-read, easy-to-write plain text
format, then convert it to structurally valid XHTML (or HTML).
Thus, “Markdown” is two things: (1) a plain text formatting syntax;
and (2) a software tool, written in Perl, that converts the plain text
formatting to HTML. See the Syntax page for details pertaining to
Markdown’s formatting syntax. You can try it out, right now, using the
online Dingus.
You can find the sytnax here