diff --git a/jedi/docstrings.py b/jedi/docstrings.py
index badb6348..a85d68f8 100644
--- a/jedi/docstrings.py
+++ b/jedi/docstrings.py
@@ -39,6 +39,17 @@ def follow_param(param):
 
 
 def search_param_in_docstr(docstr, param_str):
+    """
+    Search `docstr` for a type of `param_str`.
+
+    >>> search_param_in_docstr(':type param: int', 'param')
+    'int'
+    >>> search_param_in_docstr('@type param: int', 'param')
+    'int'
+    >>> search_param_in_docstr('no document', 'param') is None
+    True
+
+    """
     # look at #40 to see definitions of those params
     patterns = [ re.compile(p % re.escape(param_str)) for p in DOCSTRING_PARAM_PATTERNS ]
     for pattern in patterns: