State clearly that truncate() doesn't move the file position,
and remove a duplicate of its specification.
diff --git a/Doc/library/io.rst b/Doc/library/io.rst
index cf5e9f7..9f08c25 100644
--- a/Doc/library/io.rst
+++ b/Doc/library/io.rst
@@ -319,7 +319,9 @@
.. method:: truncate(size=None)
Truncate the file to at most *size* bytes. *size* defaults to the current
- file position, as returned by :meth:`tell`.
+ file position, as returned by :meth:`tell`. Note that the current file
+ position isn't changed; if you want to change it to the new end of
+ file, you have to :meth:`seek()` explicitly.
.. method:: writable()
@@ -527,11 +529,6 @@
In :class:`BytesIO`, this is the same as :meth:`read`.
- .. method:: truncate([size])
-
- Truncate the buffer to at most *size* bytes. *size* defaults to the
- current stream position, as returned by :meth:`tell`.
-
.. class:: BufferedReader(raw, buffer_size=DEFAULT_BUFFER_SIZE)