#2131: note that codecs.open() always opens files in binary mode.
diff --git a/Doc/library/codecs.rst b/Doc/library/codecs.rst
index c6dc0a3..e3f4311 100644
--- a/Doc/library/codecs.rst
+++ b/Doc/library/codecs.rst
@@ -206,7 +206,8 @@
.. function:: open(filename, mode[, encoding[, errors[, buffering]]])
Open an encoded file using the given *mode* and return a wrapped version
- providing transparent encoding/decoding.
+ providing transparent encoding/decoding. The default file mode is ``'r'``
+ meaning to open the file in read mode.
.. note::
@@ -214,6 +215,13 @@
i.e. Unicode objects for most built-in codecs. Output is also codec-dependent
and will usually be Unicode as well.
+ .. note::
+
+ Files are always opened in binary mode, even if no binary mode was
+ specified. This is done to avoid data loss due to encodings using 8-bit
+ values. This means that no automatic conversion of ``'\n'`` is done
+ on reading and writing.
+
*encoding* specifies the encoding which is to be used for the file.
*errors* may be given to define the error handling. It defaults to ``'strict'``