Issue #17398: document url argument of RobotFileParser
diff --git a/Doc/library/urllib.robotparser.rst b/Doc/library/urllib.robotparser.rst
index 0cac2ad..f179de2 100644
--- a/Doc/library/urllib.robotparser.rst
+++ b/Doc/library/urllib.robotparser.rst
@@ -19,10 +19,10 @@
structure of :file:`robots.txt` files, see http://www.robotstxt.org/orig.html.
-.. class:: RobotFileParser()
+.. class:: RobotFileParser(url='')
- This class provides a set of methods to read, parse and answer questions
- about a single :file:`robots.txt` file.
+ This class provides methods to read, parse and answer questions about the
+ :file:`robots.txt` file at *url*.
.. method:: set_url(url)