Add interface.

Michelf/Markdown.php

@@ -17,7 +17,7 @@ namespace Michelf;
 # Markdown Parser Class
 #
 
-class Markdown {
+class Markdown implements MarkdownInterface {
 
 	### Version ###
 

Michelf/MarkdownInterface.php

@@ -0,0 +1,37 @@
+<?php
+#
+# Markdown  -  A text-to-HTML conversion tool for web writers
+#
+# PHP Markdown
+# Copyright (c) 2004-2013 Michel Fortin
+# <http://michelf.com/projects/php-markdown/>
+#
+# Original Markdown
+# Copyright (c) 2004-2006 John Gruber
+# <http://daringfireball.net/projects/markdown/>
+#
+namespace Michelf;
+
+
+#
+# Markdown Parser Interface
+#
+
+interface MarkdownInterface {
+
+  #
+  # Initialize the parser and return the result of its transform method.
+  # This will work fine for derived classes too.
+  #
+  public static function defaultTransform($text);
+
+  #
+  # Main function. Performs some preprocessing on the input text
+  # and pass it through the document gamut.
+  #
+  public function transform($text);
+
+}
+
+
+?>