RTL in Markdown

Actually as my friend Aevyz reminded me, Markdown parses HTML in it.

You won't need to change your parser. The quickest path to solve that I could think of is this:

<div dir="rtl">

سلام دنیا

مرحبا العالم

שלום בעולם

ہیلو دنیا
</div>

So you need to add literally two lines to turn a whole document or an arbitrary section of it into RTL. It will be more compatible than an own script.

Not exactly markdown, but this is how you can override paragraph direction in StackExchange questions and answers (this method does not work for comments):

add &#x202b; (RIGHT-TO-LEFT EMBEDDING) in the beginning of a paragraph does control the direction of this paragraph (auto-reset on <br/> or empty line):

&#x202b;test מה זה? YES<br/>
test1 מה זה? NO
test2 מה זה? NO

&#x202b;test1 מה זה? YES
test2 מה זה? YES

‫test מה זה? YES
test1 מה זה? NO test2 מה זה? NO

‫test1 מה זה? YES test2 מה זה? YES

Here is a JavaScript implementation of Markdown, which (according to the commit comments) adds support for RTL languages, namely Arabic, Hebrew, Syriac, Thaana. And it seems trivially easy to add more languages.

https://github.com/hasenj/showdown/

It's based on Showdown, http://attacklab.net/showdown.

It seems to automatically understand whether or not to render the text from right to left.
Consider this code snippet: (from the very first commit at GitHub)

var p_tag = "<p>";
var rtl_p_tag = "<p style='direction:rtl; text-align: right'>";

// Check for RTL paragraphs: paragraphs that start with a character
// from an RTL script.
// RTL scripts are: Arabic, Hebrew, Syriac, Thaana
// Unicode ranges reference: http://www.ssec.wisc.edu/~tomw/java/unicode.html
var first_char = str.charCodeAt(str.search(/\S/)); //first non-white-space char
if(first_char >= 1424 && first_char <= 1983) 
{
    p_tag = rtl_p_tag;
}

    str = _RunSpanGamut(str);
    str = str.replace(/^([ \t]*)/g, p_tag);

Hope this helps,
Magnus