Markdown is an emerging markup language which emphasis on easy to learn and use so that the writer can focus on the content and not the formatting.
With Markdown, you use symbols to mark text as bold, or using hashtag to output different header size. You can see the basic example of markdown. I like Markdown because it's really easy to use, however, if you want to create your very own Markdown editor, this PHP library - Parsedown will be very handy for you.
Parsedown is a parser for Markdown. · ·
It reads Markdown similarly to how people do. · ·
First, it breaks texts into lines. · ·
Then, it looks at how these lines start and relate to each other. · ·
Finally, it looks for special characters to identify inline elements. · ·
As a result, Parsedown is (very) fast and consistent.