diff --git a/DependencyInjection/Configuration.php b/DependencyInjection/Configuration.php
new file mode 100644
index 0000000..08da2b3
--- /dev/null
+++ b/DependencyInjection/Configuration.php
@@ -0,0 +1,33 @@
+<?php
+
+namespace Knplabs\Bundle\MarkdownBundle\DependencyInjection;
+
+use Symfony\Component\Config\Definition\Builder\NodeBuilder;
+use Symfony\Component\Config\Definition\Builder\TreeBuilder;
+
+class Configuration
+{
+    /**
+     * Generates the configuration tree.
+     *
+     * @return \Symfony\Component\DependencyInjection\Configuration\NodeInterface
+     */
+    public function getConfigTree()
+    {
+        $treeBuilder = new TreeBuilder();
+
+        $treeBuilder->root('knplabs_markdown', 'array')
+            ->addDefaultsIfNotSet()
+            ->children()
+                ->arrayNode('parser')
+                ->addDefaultsIfNotSet()
+                    ->children()
+                        ->scalarNode('service')->cannotBeEmpty()->defaultValue('markdown.parser.max')->end()
+                    ->end()
+                ->end()
+            ->end()
+        ->end();
+
+        return $treeBuilder->buildTree();
+    }
+}
diff --git a/DependencyInjection/KnplabsMarkdownExtension.php b/DependencyInjection/KnplabsMarkdownExtension.php
index 239409c..115d47a 100644
--- a/DependencyInjection/KnplabsMarkdownExtension.php
+++ b/DependencyInjection/KnplabsMarkdownExtension.php
@@ -2,6 +2,7 @@
 
 namespace Knplabs\Bundle\MarkdownBundle\DependencyInjection;
 
+use Symfony\Component\Config\Definition\Processor;
 use Symfony\Component\HttpKernel\DependencyInjection\Extension;
 use Symfony\Component\DependencyInjection\Loader\XmlFileLoader;
 use Symfony\Component\Config\FileLocator;
@@ -17,87 +18,16 @@ class KnplabsMarkdownExtension extends Extension
      */
     public function load(array $configs , ContainerBuilder $container)
     {
-        $config = array();
-        foreach($configs as $c) {
-            $config = array_merge($config, $c);
-        }
+        $processor = new Processor();
+        $configuration = new Configuration();
 
-        if(array_key_exists('parser', $config)) {
-            $this->parserLoad($config, $container);
-        }
-        
-        if(array_key_exists('helper', $config)) {
-            $this->helperLoad($config, $container);
-        }
+        $config = $processor->process($configuration->getConfigTree(), $configs);
 
-        if(array_key_exists('twig', $config)) {
-            $this->twigLoad($config, $container);
-        }
-    }
-
-    /**
-     * Handles the parser configuration.
-     *
-     * @param array $config The configurations being loaded
-     * @param ContainerBuilder $container
-     */
-    public function parserLoad($config, ContainerBuilder $container)
-    {
         $loader = new XmlFileLoader($container, new FileLocator(__DIR__.'/../Resources/config'));
         $loader->load('parser.xml');
-
-        if(isset($config['parser']['class'])) {
-            $container->setParameter('markdown.parser.class', $config['parser']['class']);
-        }
-    }
-
-    /**
-     * Handles the helper configuration.
-     *
-     * @param array $config The configurations being loaded
-     * @param ContainerBuilder $container
-     */
-    public function helperLoad($config, ContainerBuilder $container)
-    {
-        $loader = new XmlFileLoader($container, new FileLocator(__DIR__.'/../Resources/config'));
         $loader->load('helper.xml');
-    }
-
-    /**
-     * Handles the twig configuration.
-     *
-     * @param array $config The configurations being loaded
-     * @param ContainerBuilder $container
-     */
-    public function twigLoad($config, ContainerBuilder $container)
-    {
-        $loader = new XmlFileLoader($container, new FileLocator(__DIR__.'/../Resources/config'));
         $loader->load('twig.xml');
-    }
 
-    /**
-     * Returns the base path for the XSD files.
-     *
-     * @return string The XSD base path
-     */
-    public function getXsdValidationBasePath()
-    {
-        return null;
-    }
-
-    /**
-     * @see Symfony\Component\DependencyInjection\Extension\ExtensionInterface
-     */
-    public function getNamespace()
-    {
-        return 'http://www.symfony-project.org/schema/dic/markdown';
-    }
-
-    /**
-     * @see Symfony\Component\DependencyInjection\Extension\ExtensionInterface
-     */
-    public function getAlias()
-    {
-        return 'knplabs_markdown';
+        $container->setAlias('markdown.parser', $config['parser']['service']);
     }
 }
diff --git a/MarkdownParserInterface.php b/MarkdownParserInterface.php
new file mode 100644
index 0000000..99df22e
--- /dev/null
+++ b/MarkdownParserInterface.php
@@ -0,0 +1,14 @@
+<?php
+
+namespace Knplabs\Bundle\MarkdownBundle;
+
+interface MarkdownParserInterface
+{
+    /**
+     * Converts text to html using markdown rules
+     *
+     * @param string $text plain text
+     * @return string rendered html
+     */
+    function transform($text);
+}
diff --git a/Parser/MarkdownParser.php b/Parser/MarkdownParser.php
index 5f87217..ffde4ab 100644
--- a/Parser/MarkdownParser.php
+++ b/Parser/MarkdownParser.php
@@ -2,6 +2,8 @@
 
 namespace Knplabs\Bundle\MarkdownBundle\Parser;
 
+use Knplabs\Bundle\MarkdownBundle\MarkdownParserInterface;
+
 require_once(realpath(__DIR__.'/..').'/vendor/parser/MarkdownExtraParser.php');
 
 /**
@@ -10,7 +12,7 @@ require_once(realpath(__DIR__.'/..').'/vendor/parser/MarkdownExtraParser.php');
  * This class extends the original Markdown parser.
  * It allows to disable unwanted features to increase performances.
  */
-class MarkdownParser extends \MarkdownExtraParser
+class MarkdownParser extends \MarkdownExtraParser implements MarkdownParserInterface
 {
 
     /**
diff --git a/README.markdown b/README.markdown
index 70c8b33..a90c31d 100644
--- a/README.markdown
+++ b/README.markdown
@@ -1,26 +1,12 @@
 Provide markdown conversion to your Symfony2 projects.
 
+This implementation is based on Michel Fortin work.
+We added PHP5 sugar, feature selection, and unit tests.
+
 ## INSTALLATION
 
 Put MarkdownBundle in your `src/Bundle` dir.
 
-Then enable it in your `config.yml`:
-    knplabs_markdown:
-      parser: ~      # Enable the parser service
-      helper: ~      # Enable the helper in the templates
-
-Optionnally enable the twig markdown filter :
-
-    twig: ~          # Enable Twig
-    knplabs_markdown:
-      twig: ~        # Enable the markdown filter
-
-You can also define your own Parser class :
-
-    knplabs_markdown:
-      parser:
-        class: Bundle\HelloBundle\MarkdownParser
-
 ## USAGE
 
     // Use the service
@@ -33,6 +19,25 @@ If you have enabled the twig markdown filter, you can use the following in your
 
     {{ my_data | markdown }}
 
+## Change the parser implementation
+
+Create a service implementing Knplabs\Bundle\MarkdownBundle\ParserInterface,
+then configure the bundle to use it:
+
+    knplabs_markdown:
+          parser:
+                  service: my.markdown.parser
+
+This bundle comes with 4 parser services, all based on the same algorithm
+but providing different levels of compliance to the markdown specification:
+
+- markdown.parser.max       // fully compliant = slower (default implementation)
+- markdown.parser.medium    // expensive and uncommon features dropped
+- markdown.parser.light     // expensive features dropped
+- markdown.parser.min       // most features dropped = faster
+
+For more details, see the implementations in Parser/Preset.
+
 ## TEST
 
     phpunit -c myapp src/Bundle/MarkdownBundle
diff --git a/Resources/config/helper.xml b/Resources/config/helper.xml
index 27124e9..4682751 100644
--- a/Resources/config/helper.xml
+++ b/Resources/config/helper.xml
@@ -12,9 +12,9 @@
 
   <services>
 
-    <service id="templating.helper.markdown" class="%templating.helper.markdown.class%">
+    <service id="templating.helper.markdown" class="%templating.helper.markdown.class%" public="false">
       <tag name="templating.helper" alias="markdown" />
-      <argument type="service" id="markdown_parser" />
+      <argument type="service" id="markdown.parser" />
     </service>
 
   </services>
diff --git a/Resources/config/parser.xml b/Resources/config/parser.xml
index fe94918..94958a9 100644
--- a/Resources/config/parser.xml
+++ b/Resources/config/parser.xml
@@ -4,31 +4,11 @@
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd">
 
-  <parameters>
-
-    <parameter key="markdown.parser.min.class">Knplabs\Bundle\MarkdownBundle\Parser\Preset\Min</parameter>
-    <parameter key="markdown.parser.light.class">Knplabs\Bundle\MarkdownBundle\Parser\Preset\Light</parameter>
-    <parameter key="markdown.parser.medium.class">Knplabs\Bundle\MarkdownBundle\Parser\Preset\Medium</parameter>
-    <parameter key="markdown.parser.max.class">Knplabs\Bundle\MarkdownBundle\Parser\Preset\Max</parameter>
-
-    <parameter key="markdown.parser.class">%markdown.parser.max.class%</parameter>
-
-    <parameter key="markdown.parser.features" type="collection"></parameter>
-
-    <parameter key="templating.helper.markdown.class">Knplabs\Bundle\MarkdownBundle\Helper\MarkdownHelper</parameter>
-
-  </parameters>
-
   <services>
-
-    <service id="markdown_parser" class="%markdown.parser.class%">
-      <argument type="collection">%markdown.parser.features%</argument>
-    </service>
-
-    <service id="templating.helper.markdown" class="%templating.helper.markdown.class%">
-      <argument type="service" id="markdown_parser" />
-      <tag name="templating.helper" alias="markdown" />
-    </service>
-
+      <service id="markdown.parser.min" class="Knplabs\Bundle\MarkdownBundle\Parser\Preset\Min" />
+      <service id="markdown.parser.light" class="Knplabs\Bundle\MarkdownBundle\Parser\Preset\Light" />
+      <service id="markdown.parser.medium" class="Knplabs\Bundle\MarkdownBundle\Parser\Preset\Medium" />
+      <service id="markdown.parser.max" class="Knplabs\Bundle\MarkdownBundle\Parser\Preset\Max" />
   </services>
+
 </container>
diff --git a/Resources/config/twig.xml b/Resources/config/twig.xml
index cc6d1ef..c958ad3 100644
--- a/Resources/config/twig.xml
+++ b/Resources/config/twig.xml
@@ -5,7 +5,7 @@
     xsi:schemaLocation="http://symfony.com/schema/dic/services http://symfony.com/schema/dic/services/services-1.0.xsd">
 
     <services>
-        <service id="twig.extension.exercise.twig" class="Knplabs\Bundle\MarkdownBundle\Twig\Extension\MarkdownTwigExtension">
+        <service id="twig.extension.exercise.twig" class="Knplabs\Bundle\MarkdownBundle\Twig\Extension\MarkdownTwigExtension" public="false">
             <argument type="service" id="templating.helper.markdown" />
             <tag name="twig.extension" />
         </service>