diff --git a/src/Symfony/Component/Validator/Mapping/Loader/AbstractLoader.php b/src/Symfony/Component/Validator/Mapping/Loader/AbstractLoader.php
index d403f28c13..a69752d6df 100644
--- a/src/Symfony/Component/Validator/Mapping/Loader/AbstractLoader.php
+++ b/src/Symfony/Component/Validator/Mapping/Loader/AbstractLoader.php
@@ -14,11 +14,25 @@ namespace Symfony\Component\Validator\Mapping\Loader;
 use Symfony\Component\Validator\Exception\MappingException;
 use Symfony\Component\Validator\Constraint;
 
+/**
+ * Base loader for validation metadata.
+ *
+ * This loader supports the loading of constraints from Symfony's default
+ * namespace (see {@link DEFAULT_NAMESPACE}) using the short class names of
+ * those constraints. Constraints can also be loaded using their fully
+ * qualified class names. At last, namespace aliases can be defined to load
+ * constraints with the syntax "alias:ShortName".
+ *
+ * @author Bernhard Schussek <bschussek@gmail.com>
+ */
 abstract class AbstractLoader implements LoaderInterface
 {
     /**
-     * Contains all known namespaces indexed by their prefix.
-     *
+     * The namespace to load constraints from by default.
+     */
+    const DEFAULT_NAMESPACE = '\\Symfony\\Component\\Validator\\Constraints\\';
+
+    /**
      * @var array
      */
     protected $namespaces;
@@ -26,6 +40,13 @@ abstract class AbstractLoader implements LoaderInterface
     /**
      * Adds a namespace alias.
      *
+     * The namespace alias can be used to reference constraints from specific
+     * namespaces in {@link newConstraint()}:
+     *
+     *     $this->addNamespaceAlias('mynamespace', '\\Acme\\Package\\Constraints\\');
+     *
+     *     $constraint = $this->newConstraint('mynamespace:NotNull');
+     *
      * @param string $alias     The alias
      * @param string $namespace The PHP namespace
      */
@@ -37,16 +58,19 @@ abstract class AbstractLoader implements LoaderInterface
     /**
      * Creates a new constraint instance for the given constraint name.
      *
-     * @param string $name    The constraint name. Either a constraint relative
-     *                        to the default constraint namespace, or a fully
-     *                        qualified class name
-     * @param mixed  $options The constraint options
+     * @param string $name   The constraint name. Either a constraint relative
+     *                       to the default constraint namespace, or a fully
+     *                       qualified class name. Alternatively, the constraint
+     *                       may be preceded by a namespace alias and a colon.
+     *                       The namespace alias must have been defined using
+     *                       {@link addNamespaceAlias()}.
+     * @param mixed $options The constraint options
      *
      * @return Constraint
      *
      * @throws MappingException If the namespace prefix is undefined
      */
-    protected function newConstraint($name, $options)
+    protected function newConstraint($name, $options = null)
     {
         if (strpos($name, '\\') !== false && class_exists($name)) {
             $className = (string) $name;
@@ -59,7 +83,7 @@ abstract class AbstractLoader implements LoaderInterface
 
             $className = $this->namespaces[$prefix].$className;
         } else {
-            $className = 'Symfony\\Component\\Validator\\Constraints\\'.$name;
+            $className = self::DEFAULT_NAMESPACE.$name;
         }
 
         return new $className($options);
diff --git a/src/Symfony/Component/Validator/Mapping/Loader/AnnotationLoader.php b/src/Symfony/Component/Validator/Mapping/Loader/AnnotationLoader.php
index ac04f61774..bb96be6354 100644
--- a/src/Symfony/Component/Validator/Mapping/Loader/AnnotationLoader.php
+++ b/src/Symfony/Component/Validator/Mapping/Loader/AnnotationLoader.php
@@ -18,23 +18,40 @@ use Symfony\Component\Validator\Constraints\GroupSequence;
 use Symfony\Component\Validator\Constraints\GroupSequenceProvider;
 use Symfony\Component\Validator\Constraint;
 
+/**
+ * Loads validation metadata using a Doctrine annotation {@link Reader}.
+ *
+ * @author Bernhard Schussek <bschussek@gmail.com>
+ */
 class AnnotationLoader implements LoaderInterface
 {
+    /**
+     * @var Reader
+     */
     protected $reader;
 
+    /**
+     * Creates a new loader.
+     *
+     * @param Reader $reader The annotation reader to use.
+     */
     public function __construct(Reader $reader)
     {
         $this->reader = $reader;
     }
 
     /**
-     * {@inheritdoc}
+     * Loads the metadata using annotations defined in the class.
+     *
+     * @param ClassMetadata $metadata The class metadata to load
+     *
+     * @return bool Whether the loader succeeded
      */
     public function loadClassMetadata(ClassMetadata $metadata)
     {
         $reflClass = $metadata->getReflectionClass();
         $className = $reflClass->name;
-        $loaded = false;
+        $success = false;
 
         foreach ($this->reader->getClassAnnotations($reflClass) as $constraint) {
             if ($constraint instanceof GroupSequence) {
@@ -45,7 +62,7 @@ class AnnotationLoader implements LoaderInterface
                 $metadata->addConstraint($constraint);
             }
 
-            $loaded = true;
+            $success = true;
         }
 
         foreach ($reflClass->getProperties() as $property) {
@@ -55,7 +72,7 @@ class AnnotationLoader implements LoaderInterface
                         $metadata->addPropertyConstraint($property->name, $constraint);
                     }
 
-                    $loaded = true;
+                    $success = true;
                 }
             }
         }
@@ -71,11 +88,11 @@ class AnnotationLoader implements LoaderInterface
                         }
                     }
 
-                    $loaded = true;
+                    $success = true;
                 }
             }
         }
 
-        return $loaded;
+        return $success;
     }
 }
diff --git a/src/Symfony/Component/Validator/Mapping/Loader/FileLoader.php b/src/Symfony/Component/Validator/Mapping/Loader/FileLoader.php
index 2b8c6c04c0..326bbdfe75 100644
--- a/src/Symfony/Component/Validator/Mapping/Loader/FileLoader.php
+++ b/src/Symfony/Component/Validator/Mapping/Loader/FileLoader.php
@@ -13,26 +13,42 @@ namespace Symfony\Component\Validator\Mapping\Loader;
 
 use Symfony\Component\Validator\Exception\MappingException;
 
+/**
+ * Base loader for loading validation metadata from a file.
+ *
+ * @author Bernhard Schussek <bschussek@gmail.com>
+ *
+ * @see YamlFileLoader
+ * @see XmlFileLoader
+ */
 abstract class FileLoader extends AbstractLoader
 {
+    /**
+     * The file to load.
+     *
+     * @var string
+     */
     protected $file;
 
     /**
-     * Constructor.
+     * Creates a new loader.
      *
      * @param string $file The mapping file to load
      *
-     * @throws MappingException if the mapping file does not exist
-     * @throws MappingException if the mapping file is not readable
+     * @throws MappingException If the file does not exist or is not readable
      */
     public function __construct($file)
     {
         if (!is_file($file)) {
-            throw new MappingException(sprintf('The mapping file %s does not exist', $file));
+            throw new MappingException(sprintf('The mapping file "%s" does not exist', $file));
         }
 
         if (!is_readable($file)) {
-            throw new MappingException(sprintf('The mapping file %s is not readable', $file));
+            throw new MappingException(sprintf('The mapping file "%s" is not readable', $file));
+        }
+
+        if (!stream_is_local($this->file)) {
+            throw new MappingException(sprintf('The mapping file "%s" is not a local file', $file));
         }
 
         $this->file = $file;
diff --git a/src/Symfony/Component/Validator/Mapping/Loader/FilesLoader.php b/src/Symfony/Component/Validator/Mapping/Loader/FilesLoader.php
index a631093296..e82d7ed189 100644
--- a/src/Symfony/Component/Validator/Mapping/Loader/FilesLoader.php
+++ b/src/Symfony/Component/Validator/Mapping/Loader/FilesLoader.php
@@ -12,21 +12,25 @@
 namespace Symfony\Component\Validator\Mapping\Loader;
 
 /**
- * Creates mapping loaders for array of files.
- *
- * Abstract class, used by
+ * Base loader for loading validation metadata from a list of files.
  *
  * @author Bulat Shakirzyanov <mallluhuct@gmail.com>
+ * @author Bernhard Schussek <bschussek@gmail.com>
  *
+<<<<<<< HEAD
  * @see YamlFileLoader
  * @see XmlFileLoader
+=======
+ * @see YamlFilesLoader
+ * @see XmlFilesLoader
+>>>>>>> pull/12201
  */
 abstract class FilesLoader extends LoaderChain
 {
     /**
-     * Array of mapping files.
+     * Creates a new loader.
      *
-     * @param array $paths Array of file paths
+     * @param array $paths An array of file paths
      */
     public function __construct(array $paths)
     {
@@ -34,15 +38,16 @@ abstract class FilesLoader extends LoaderChain
     }
 
     /**
-     * Array of mapping files.
+     * Returns an array of file loaders for the given file paths.
      *
-     * @param array $paths Array of file paths
+     * @param array $paths An array of file paths
      *
-     * @return LoaderInterface[] Array of metadata loaders
+     * @return LoaderInterface[] The metadata loaders
      */
     protected function getFileLoaders($paths)
     {
         $loaders = array();
+
         foreach ($paths as $path) {
             $loaders[] = $this->getFileLoaderInstance($path);
         }
@@ -51,11 +56,11 @@ abstract class FilesLoader extends LoaderChain
     }
 
     /**
-     * Takes mapping file path.
+     * Creates a loader for the given file path.
      *
-     * @param string $file
+     * @param string $path The file path
      *
-     * @return LoaderInterface
+     * @return LoaderInterface The created loader
      */
-    abstract protected function getFileLoaderInstance($file);
+    abstract protected function getFileLoaderInstance($path);
 }
diff --git a/src/Symfony/Component/Validator/Mapping/Loader/LoaderChain.php b/src/Symfony/Component/Validator/Mapping/Loader/LoaderChain.php
index c3cacdb4ba..45744894c7 100644
--- a/src/Symfony/Component/Validator/Mapping/Loader/LoaderChain.php
+++ b/src/Symfony/Component/Validator/Mapping/Loader/LoaderChain.php
@@ -15,25 +15,25 @@ use Symfony\Component\Validator\Exception\MappingException;
 use Symfony\Component\Validator\Mapping\ClassMetadata;
 
 /**
- * Calls multiple LoaderInterface instances in a chain.
+ * Loads validation metadata from multiple {@link LoaderInterface} instances.
  *
- * This class accepts multiple instances of LoaderInterface to be passed to the
- * constructor. When loadClassMetadata() is called, the same method is called
- * in <em>all</em> of these loaders, regardless of whether any of them was
- * successful or not.
+ * Pass the loaders when constructing the chain. Once
+ * {@link loadClassMetadata()} is called, that method will be called on all
+ * loaders in the chain.
  *
  * @author Bernhard Schussek <bschussek@gmail.com>
  */
 class LoaderChain implements LoaderInterface
 {
+    /**
+     * @var LoaderInterface[]
+     */
     protected $loaders;
 
     /**
-     * Accepts a list of LoaderInterface instances.
+     * @param LoaderInterface[] $loaders The metadata loaders to use
      *
-     * @param LoaderInterface[] $loaders An array of LoaderInterface instances
-     *
-     * @throws MappingException If any of the loaders does not implement LoaderInterface
+     * @throws MappingException If any of the loaders has an invalid type
      */
     public function __construct(array $loaders)
     {
@@ -47,7 +47,12 @@ class LoaderChain implements LoaderInterface
     }
 
     /**
-     * {@inheritdoc}
+     * Calls {@link LoaderInterface::loadClassMetadata()} on all loaders in
+     * the chain.
+     *
+     * @param ClassMetadata $metadata The metadata to load
+     *
+     * @return bool Whether the loader succeeded
      */
     public function loadClassMetadata(ClassMetadata $metadata)
     {
diff --git a/src/Symfony/Component/Validator/Mapping/Loader/LoaderInterface.php b/src/Symfony/Component/Validator/Mapping/Loader/LoaderInterface.php
index 43358ad1d9..5dadc82eb8 100644
--- a/src/Symfony/Component/Validator/Mapping/Loader/LoaderInterface.php
+++ b/src/Symfony/Component/Validator/Mapping/Loader/LoaderInterface.php
@@ -13,14 +13,19 @@ namespace Symfony\Component\Validator\Mapping\Loader;
 
 use Symfony\Component\Validator\Mapping\ClassMetadata;
 
+/**
+ * Loads validation metadata into {@link ClassMetadata} instances.
+ *
+ * @author Bernhard Schussek <bschussek@gmail.com>
+ */
 interface LoaderInterface
 {
     /**
-     * Load a Class Metadata.
+     * Loads validation metadata into a {@link ClassMetadata} instance.
      *
-     * @param ClassMetadata $metadata A metadata
+     * @param ClassMetadata $metadata The metadata to load
      *
-     * @return bool
+     * @return bool Whether the loader succeeded
      */
     public function loadClassMetadata(ClassMetadata $metadata);
 }
diff --git a/src/Symfony/Component/Validator/Mapping/Loader/StaticMethodLoader.php b/src/Symfony/Component/Validator/Mapping/Loader/StaticMethodLoader.php
index 54dcc57cc7..ee87ef5eeb 100644
--- a/src/Symfony/Component/Validator/Mapping/Loader/StaticMethodLoader.php
+++ b/src/Symfony/Component/Validator/Mapping/Loader/StaticMethodLoader.php
@@ -14,17 +14,38 @@ namespace Symfony\Component\Validator\Mapping\Loader;
 use Symfony\Component\Validator\Exception\MappingException;
 use Symfony\Component\Validator\Mapping\ClassMetadata;
 
+/**
+ * Loads validation metadata by calling a static method on the loaded class.
+ *
+ * @author Bernhard Schussek <bschussek@gmail.com>
+ */
 class StaticMethodLoader implements LoaderInterface
 {
+    /**
+     * The name of the method to call.
+     *
+     * @var string
+     */
     protected $methodName;
 
+    /**
+     * Creates a new loader.
+     *
+     * @param string $methodName The name of the static method to call
+     */
     public function __construct($methodName = 'loadValidatorMetadata')
     {
         $this->methodName = $methodName;
     }
 
     /**
-     * {@inheritdoc}
+     * Loads validation metadata by calling a static method in the class.
+     *
+     * The name of the static method is passed to {@link __construct()}.
+     *
+     * @param ClassMetadata $metadata The metadata to load
+     *
+     * @return bool Whether the loader succeeded
      */
     public function loadClassMetadata(ClassMetadata $metadata)
     {
diff --git a/src/Symfony/Component/Validator/Mapping/Loader/XmlFileLoader.php b/src/Symfony/Component/Validator/Mapping/Loader/XmlFileLoader.php
index c7d82c449c..45dcb4f237 100644
--- a/src/Symfony/Component/Validator/Mapping/Loader/XmlFileLoader.php
+++ b/src/Symfony/Component/Validator/Mapping/Loader/XmlFileLoader.php
@@ -15,24 +15,36 @@ use Symfony\Component\Validator\Exception\MappingException;
 use Symfony\Component\Validator\Mapping\ClassMetadata;
 use Symfony\Component\Config\Util\XmlUtils;
 
+/**
+ * Loads validation metadata from an XML file.
+ *
+ * @author Bernhard Schussek <bschussek@gmail.com>
+ */
 class XmlFileLoader extends FileLoader
 {
     /**
-     * An array of SimpleXMLElement instances.
+     * The XML nodes of the mapping file.
      *
      * @var \SimpleXMLElement[]
      */
     protected $classes = null;
 
     /**
-     * {@inheritdoc}
+     * Loads validation metadata using the metadata defined in the XML file.
+     *
+     * @param ClassMetadata $metadata The metadata to load
+     *
+     * @return bool Whether the loader succeeded
      */
     public function loadClassMetadata(ClassMetadata $metadata)
     {
         if (null === $this->classes) {
-            $this->classes = array();
+            // This method may throw an exception. Do not modify the class'
+            // state before it completes
             $xml = $this->parseFile($this->file);
 
+            $this->classes = array();
+
             foreach ($xml->namespace as $namespace) {
                 $this->addNamespaceAlias((string) $namespace['prefix'], trim((string) $namespace));
             }
@@ -43,33 +55,9 @@ class XmlFileLoader extends FileLoader
         }
 
         if (isset($this->classes[$metadata->getClassName()])) {
-            $xml = $this->classes[$metadata->getClassName()];
+            $classDescription = $this->classes[$metadata->getClassName()];
 
-            foreach ($xml->{'group-sequence-provider'} as $provider) {
-                $metadata->setGroupSequenceProvider(true);
-            }
-
-            foreach ($xml->{'group-sequence'} as $groupSequence) {
-                if (count($groupSequence->value) > 0) {
-                    $metadata->setGroupSequence($this->parseValues($groupSequence[0]->value));
-                }
-            }
-
-            foreach ($this->parseConstraints($xml->constraint) as $constraint) {
-                $metadata->addConstraint($constraint);
-            }
-
-            foreach ($xml->property as $property) {
-                foreach ($this->parseConstraints($property->constraint) as $constraint) {
-                    $metadata->addPropertyConstraint((string) $property['name'], $constraint);
-                }
-            }
-
-            foreach ($xml->getter as $getter) {
-                foreach ($this->parseConstraints($getter->constraint) as $constraint) {
-                    $metadata->addGetterConstraint((string) $getter['property'], $constraint);
-                }
-            }
+            $this->loadClassMetadataFromXml($metadata, $classDescription);
 
             return true;
         }
@@ -179,22 +167,57 @@ class XmlFileLoader extends FileLoader
     }
 
     /**
-     * Parse a XML File.
+     * Loads the XML class descriptions from the given file.
      *
-     * @param string $file Path of file
+     * @param string $path The path of the XML file
      *
-     * @return \SimpleXMLElement
+     * @return \SimpleXMLElement The class descriptions
      *
-     * @throws MappingException
+     * @throws MappingException If the file could not be loaded
      */
-    protected function parseFile($file)
+    protected function parseFile($path)
     {
         try {
-            $dom = XmlUtils::loadFile($file, __DIR__.'/schema/dic/constraint-mapping/constraint-mapping-1.0.xsd');
+            $dom = XmlUtils::loadFile($path, __DIR__.'/schema/dic/constraint-mapping/constraint-mapping-1.0.xsd');
         } catch (\Exception $e) {
             throw new MappingException($e->getMessage(), $e->getCode(), $e);
         }
 
         return simplexml_import_dom($dom);
     }
+
+    /**
+     * Loads the validation metadata from the given XML class description.
+     *
+     * @param ClassMetadata $metadata         The metadata to load
+     * @param array         $classDescription The XML class description
+     */
+    private function loadClassMetadataFromXml(ClassMetadata $metadata, $classDescription)
+    {
+        foreach ($classDescription->{'group-sequence-provider'} as $_) {
+            $metadata->setGroupSequenceProvider(true);
+        }
+
+        foreach ($classDescription->{'group-sequence'} as $groupSequence) {
+            if (count($groupSequence->value) > 0) {
+                $metadata->setGroupSequence($this->parseValues($groupSequence[0]->value));
+            }
+        }
+
+        foreach ($this->parseConstraints($classDescription->constraint) as $constraint) {
+            $metadata->addConstraint($constraint);
+        }
+
+        foreach ($classDescription->property as $property) {
+            foreach ($this->parseConstraints($property->constraint) as $constraint) {
+                $metadata->addPropertyConstraint((string) $property['name'], $constraint);
+            }
+        }
+
+        foreach ($classDescription->getter as $getter) {
+            foreach ($this->parseConstraints($getter->constraint) as $constraint) {
+                $metadata->addGetterConstraint((string) $getter['property'], $constraint);
+            }
+        }
+    }
 }
diff --git a/src/Symfony/Component/Validator/Mapping/Loader/XmlFilesLoader.php b/src/Symfony/Component/Validator/Mapping/Loader/XmlFilesLoader.php
index 3b7043feaf..6017c3f44d 100644
--- a/src/Symfony/Component/Validator/Mapping/Loader/XmlFilesLoader.php
+++ b/src/Symfony/Component/Validator/Mapping/Loader/XmlFilesLoader.php
@@ -12,9 +12,10 @@
 namespace Symfony\Component\Validator\Mapping\Loader;
 
 /**
- * Loads multiple xml mapping files.
+ * Loads validation metadata from a list of XML files.
  *
  * @author Bulat Shakirzyanov <mallluhuct@gmail.com>
+ * @author Bernhard Schussek <bschussek@gmail.com>
  *
  * @see FilesLoader
  */
diff --git a/src/Symfony/Component/Validator/Mapping/Loader/YamlFileLoader.php b/src/Symfony/Component/Validator/Mapping/Loader/YamlFileLoader.php
index 2737ccadb3..34699fce1b 100644
--- a/src/Symfony/Component/Validator/Mapping/Loader/YamlFileLoader.php
+++ b/src/Symfony/Component/Validator/Mapping/Loader/YamlFileLoader.php
@@ -14,10 +14,13 @@ namespace Symfony\Component\Validator\Mapping\Loader;
 use Symfony\Component\Validator\Mapping\ClassMetadata;
 use Symfony\Component\Yaml\Parser as YamlParser;
 
+/**
+ * Loads validation metadata from a YAML file.
+ *
+ * @author Bernhard Schussek <bschussek@gmail.com>
+ */
 class YamlFileLoader extends FileLoader
 {
-    private $yamlParser;
-
     /**
      * An array of YAML class descriptions.
      *
@@ -26,34 +29,33 @@ class YamlFileLoader extends FileLoader
     protected $classes = null;
 
     /**
-     * {@inheritdoc}
+     * Caches the used YAML parser.
+     *
+     * @var YamlParser
+     */
+    private $yamlParser;
+
+    /**
+     * Loads validation metadata using the metadata defined in the YAML file.
+     *
+     * @param ClassMetadata $metadata The metadata to load
+     *
+     * @return bool Whether the loader succeeded
      */
     public function loadClassMetadata(ClassMetadata $metadata)
     {
         if (null === $this->classes) {
-            if (!stream_is_local($this->file)) {
-                throw new \InvalidArgumentException(sprintf('This is not a local file "%s".', $this->file));
-            }
-
-            if (!file_exists($this->file)) {
-                throw new \InvalidArgumentException(sprintf('File "%s" not found.', $this->file));
-            }
-
             if (null === $this->yamlParser) {
                 $this->yamlParser = new YamlParser();
             }
 
-            $this->classes = $this->yamlParser->parse(file_get_contents($this->file));
-
-            // empty file
-            if (null === $this->classes) {
+            // This method may throw an exception. Do not modify the class'
+            // state before it completes
+            if (false === ($classes = $this->parseFile($this->file))) {
                 return false;
             }
 
-            // not an array
-            if (!is_array($this->classes)) {
-                throw new \InvalidArgumentException(sprintf('The file "%s" must contain a YAML array.', $this->file));
-            }
+            $this->classes = $classes;
 
             if (isset($this->classes['namespaces'])) {
                 foreach ($this->classes['namespaces'] as $alias => $namespace) {
@@ -64,44 +66,10 @@ class YamlFileLoader extends FileLoader
             }
         }
 
-        // TODO validation
-
         if (isset($this->classes[$metadata->getClassName()])) {
-            $yaml = $this->classes[$metadata->getClassName()];
+            $classDescription = $this->classes[$metadata->getClassName()];
 
-            if (isset($yaml['group_sequence_provider'])) {
-                $metadata->setGroupSequenceProvider((bool) $yaml['group_sequence_provider']);
-            }
-
-            if (isset($yaml['group_sequence'])) {
-                $metadata->setGroupSequence($yaml['group_sequence']);
-            }
-
-            if (isset($yaml['constraints']) && is_array($yaml['constraints'])) {
-                foreach ($this->parseNodes($yaml['constraints']) as $constraint) {
-                    $metadata->addConstraint($constraint);
-                }
-            }
-
-            if (isset($yaml['properties']) && is_array($yaml['properties'])) {
-                foreach ($yaml['properties'] as $property => $constraints) {
-                    if (null !== $constraints) {
-                        foreach ($this->parseNodes($constraints) as $constraint) {
-                            $metadata->addPropertyConstraint($property, $constraint);
-                        }
-                    }
-                }
-            }
-
-            if (isset($yaml['getters']) && is_array($yaml['getters'])) {
-                foreach ($yaml['getters'] as $getter => $constraints) {
-                    if (null !== $constraints) {
-                        foreach ($this->parseNodes($constraints) as $constraint) {
-                            $metadata->addGetterConstraint($getter, $constraint);
-                        }
-                    }
-                }
-            }
+            $this->loadClassMetadataFromYaml($metadata, $classDescription);
 
             return true;
         }
@@ -140,4 +108,76 @@ class YamlFileLoader extends FileLoader
 
         return $values;
     }
+
+    /**
+     * Loads the YAML class descriptions from the given file.
+     *
+     * @param string $path The path of the YAML file
+     *
+     * @return array|null The class descriptions or null, if the file was empty
+     *
+     * @throws \InvalidArgumentException If the file could not be loaded or did
+     *                                   not contain a YAML array
+     */
+    private function parseFile($path)
+    {
+        $classes = $this->yamlParser->parse(file_get_contents($path));
+
+        // empty file
+        if (null === $classes) {
+            return;
+        }
+
+        // not an array
+        if (!is_array($classes)) {
+            throw new \InvalidArgumentException(sprintf('The file "%s" must contain a YAML array.', $this->file));
+        }
+
+        return $classes;
+    }
+
+    /**
+     * Loads the validation metadata from the given YAML class description.
+     *
+     * @param ClassMetadata $metadata         The metadata to load
+     * @param array         $classDescription The YAML class description
+     */
+    private function loadClassMetadataFromYaml(ClassMetadata $metadata, array $classDescription)
+    {
+        if (isset($classDescription['group_sequence_provider'])) {
+            $metadata->setGroupSequenceProvider(
+                (bool) $classDescription['group_sequence_provider']
+            );
+        }
+
+        if (isset($classDescription['group_sequence'])) {
+            $metadata->setGroupSequence($classDescription['group_sequence']);
+        }
+
+        if (isset($classDescription['constraints']) && is_array($classDescription['constraints'])) {
+            foreach ($this->parseNodes($classDescription['constraints']) as $constraint) {
+                $metadata->addConstraint($constraint);
+            }
+        }
+
+        if (isset($classDescription['properties']) && is_array($classDescription['properties'])) {
+            foreach ($classDescription['properties'] as $property => $constraints) {
+                if (null !== $constraints) {
+                    foreach ($this->parseNodes($constraints) as $constraint) {
+                        $metadata->addPropertyConstraint($property, $constraint);
+                    }
+                }
+            }
+        }
+
+        if (isset($classDescription['getters']) && is_array($classDescription['getters'])) {
+            foreach ($classDescription['getters'] as $getter => $constraints) {
+                if (null !== $constraints) {
+                    foreach ($this->parseNodes($constraints) as $constraint) {
+                        $metadata->addGetterConstraint($getter, $constraint);
+                    }
+                }
+            }
+        }
+    }
 }
diff --git a/src/Symfony/Component/Validator/Mapping/Loader/YamlFilesLoader.php b/src/Symfony/Component/Validator/Mapping/Loader/YamlFilesLoader.php
index e01def2f67..235856f5b9 100644
--- a/src/Symfony/Component/Validator/Mapping/Loader/YamlFilesLoader.php
+++ b/src/Symfony/Component/Validator/Mapping/Loader/YamlFilesLoader.php
@@ -12,9 +12,10 @@
 namespace Symfony\Component\Validator\Mapping\Loader;
 
 /**
- * Loads multiple yaml mapping files.
+ * Loads validation metadata from a list of YAML files.
  *
  * @author Bulat Shakirzyanov <mallluhuct@gmail.com>
+ * @author Bernhard Schussek <bschussek@gmail.com>
  *
  * @see FilesLoader
  */
diff --git a/src/Symfony/Component/Validator/Tests/Mapping/Loader/XmlFileLoaderTest.php b/src/Symfony/Component/Validator/Tests/Mapping/Loader/XmlFileLoaderTest.php
index 7c6e355bd1..9efbb46b82 100644
--- a/src/Symfony/Component/Validator/Tests/Mapping/Loader/XmlFileLoaderTest.php
+++ b/src/Symfony/Component/Validator/Tests/Mapping/Loader/XmlFileLoaderTest.php
@@ -17,6 +17,7 @@ use Symfony\Component\Validator\Constraints\NotNull;
 use Symfony\Component\Validator\Constraints\Range;
 use Symfony\Component\Validator\Constraints\Choice;
 use Symfony\Component\Validator\Constraints\Regex;
+use Symfony\Component\Validator\Exception\MappingException;
 use Symfony\Component\Validator\Mapping\ClassMetadata;
 use Symfony\Component\Validator\Mapping\Loader\XmlFileLoader;
 use Symfony\Component\Validator\Tests\Fixtures\ConstraintA;
@@ -98,15 +99,28 @@ class XmlFileLoaderTest extends \PHPUnit_Framework_TestCase
         $this->assertEquals($expected, $metadata);
     }
 
-    /**
-     * @expectedException        \Symfony\Component\Validator\Exception\MappingException
-     * @expectedExceptionMessage Document types are not allowed.
-     */
-    public function testDocTypeIsNotAllowed()
+    public function testThrowExceptionIfDocTypeIsSet()
     {
         $loader = new XmlFileLoader(__DIR__.'/withdoctype.xml');
         $metadata = new ClassMetadata('Symfony\Component\Validator\Tests\Fixtures\Entity');
 
+        $this->setExpectedException('\Symfony\Component\Validator\Exception\MappingException');
         $loader->loadClassMetadata($metadata);
     }
+
+    /**
+     * @see https://github.com/symfony/symfony/pull/12158
+     */
+    public function testDoNotModifyStateIfExceptionIsThrown()
+    {
+        $loader = new XmlFileLoader(__DIR__.'/withdoctype.xml');
+        $metadata = new ClassMetadata('Symfony\Component\Validator\Tests\Fixtures\Entity');
+
+        try {
+            $loader->loadClassMetadata($metadata);
+        } catch (MappingException $e) {
+            $this->setExpectedException('\Symfony\Component\Validator\Exception\MappingException');
+            $loader->loadClassMetadata($metadata);
+        }
+    }
 }
diff --git a/src/Symfony/Component/Validator/Tests/Mapping/Loader/YamlFileLoaderTest.php b/src/Symfony/Component/Validator/Tests/Mapping/Loader/YamlFileLoaderTest.php
index dd394acaf0..c5b39173e5 100644
--- a/src/Symfony/Component/Validator/Tests/Mapping/Loader/YamlFileLoaderTest.php
+++ b/src/Symfony/Component/Validator/Tests/Mapping/Loader/YamlFileLoaderTest.php
@@ -31,16 +31,31 @@ class YamlFileLoaderTest extends \PHPUnit_Framework_TestCase
         $this->assertFalse($loader->loadClassMetadata($metadata));
     }
 
-    /**
-     * @expectedException \InvalidArgumentException
-     */
     public function testLoadClassMetadataThrowsExceptionIfNotAnArray()
     {
         $loader = new YamlFileLoader(__DIR__.'/nonvalid-mapping.yml');
         $metadata = new ClassMetadata('Symfony\Component\Validator\Tests\Fixtures\Entity');
+
+        $this->setExpectedException('\InvalidArgumentException');
         $loader->loadClassMetadata($metadata);
     }
 
+    /**
+     * @see https://github.com/symfony/symfony/pull/12158
+     */
+    public function testDoNotModifyStateIfExceptionIsThrown()
+    {
+        $loader = new YamlFileLoader(__DIR__.'/nonvalid-mapping.yml');
+        $metadata = new ClassMetadata('Symfony\Component\Validator\Tests\Fixtures\Entity');
+        try {
+            $loader->loadClassMetadata($metadata);
+        } catch (\InvalidArgumentException $e) {
+            // Call again. Again an exception should be thrown
+            $this->setExpectedException('\InvalidArgumentException');
+            $loader->loadClassMetadata($metadata);
+        }
+    }
+
     public function testLoadClassMetadataReturnsTrueIfSuccessful()
     {
         $loader = new YamlFileLoader(__DIR__.'/constraint-mapping.yml');