How to make a paragraph from a line starting with plus sign (+)

I'am doing a simple text editor that I need to handle creating paragraphs.

Paragraphs will be in WikiDot Syntax, long story short what i need to change:

+ paragraph 1 

changes to < h1>paragraph< /h1>

++ subparagraph 1 

changes to < h2>subparagraph< /h2>

How do t开发者_Python百科his in PHP?

To expand on @CrayonViolent's (in cases where the first replace interrups the second):

<?php
  $content = "Hello, world

+ Big Heading

++ Smaller heading

Additional content";

   function r($m){
     $tag = "h".strlen($m[1]);
     return "<{$tag}>{$m[2]}</{$tag}>";
   }
   $content = preg_replace_callback('/^(\+{1,6})\s?(.*)$/m','r', $content);

   echo $content;
?>

Also added the m (multi-line) flag to the regex for a little better matching, and will only do headers <h1>~<h6>.

Working example can be located here

$content = preg_replace ("~^\+\+(.*?)\n\n~",'<h2>$1</h2>',$content);
$content = preg_replace ("~^\+(.*?)\n\n~",'<h1>$1</h1>',$content);