PHP Markdown

This snippet of code transforms a markdown string of text into the desired HTML output.
It is the same basic style of formatting that sites like github and Google+ do.
You can easily customize the inputs/outputs of the HTML code that it transforms.

	<?
	function markDown($str){
	//Tag like markdown, ordered by precedence.
	//This is the only thing you really need to configure.
	//It's a regular expression (without delimiters) as the key and the desired output as the value.
	$markdownSet = array(
	"\_\*(.*)\*_" => " <b><i>$2</i></b> ",
	"\*_(.*)_\*" => " <b><i>$2</i></b> ",
	"_(.*)_" => " <i>$2</i> ",
	"\*(.*)\*" => " <b>$2</b> ",
	"\#\#\#(.*)\#\#\#" => " <h3>$2</h3> ",
	"\#\#(.*)\#\#" => " <h2>$2</h2> ",
	"\#(.*)\#" => " <h1>$2</h1> "
	);
	//Strip out the HTML tags, replace them with text
	$str = preg_replace('/</','&lt;',$str);
	$str = preg_replace('/>/','&gt;',$str);
	//Just to make sure they're all gone.
	$str = strip_tags($str);
	foreach($markdownSet as $match => $result){
	$str = preg_replace("/([[:space:]]|\n|^)".$match."([[:space:]]|\n|$)/U","$1".$result."$3",$str);
	}
	//Make links into links
	$str = preg_replace("/http([s]?):\/\/([^\ \)\n$]*)/i","<a href='\\0' rel='nofollow'>\\0</a>",$str);
	//Make Newlines into breaks
	$str = nl2br($str);
	return $str;
	}
	?>

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