diff --git a/testinfra/modules/file.py b/testinfra/modules/file.py
index 8f8e9d2b..9fe0f8ab 100644
--- a/testinfra/modules/file.py
+++ b/testinfra/modules/file.py
@@ -116,6 +116,10 @@ def mode(self):
         raise NotImplementedError
 
     def contains(self, pattern):
+        """Checks content of file for pattern
+
+        This uses grep and thus follows the grep regex syntax.
+        """
         return self.run_test("grep -qs -- %s %s", pattern, self.path).rc == 0
 
     @property