--- a/src/pyams_file/interfaces/__init__.py	Thu Jun 08 11:03:23 2017 +0200
+++ b/src/pyams_file/interfaces/__init__.py	Wed Jul 12 12:04:31 2017 +0200
@@ -272,3 +272,10 @@
 
     def add_watermark(self, image, watermark, position='scale', opacity=1, format=None):
         """Add watermark to given image"""
+
+
+class IFileModifierForm(Interface):
+    """File modifier form marker interface
+
+    These forms have a custom context permission checker.
+    """