#25495: Clarify b2a_base64 documentation vis 57 bytes.
diff --git a/Doc/library/binascii.rst b/Doc/library/binascii.rst
index e3f134b..dbe535d 100644
--- a/Doc/library/binascii.rst
+++ b/Doc/library/binascii.rst
@@ -55,8 +55,10 @@
.. function:: b2a_base64(data)
Convert binary data to a line of ASCII characters in base64 coding. The return
- value is the converted line, including a newline char. The length of *data*
- should be at most 57 to adhere to the base64 standard.
+ value is the converted line, including a newline char. The newline is
+ added because the original use case for this function was to feed it a
+ series of 57 byte input lines to get output lines that conform to the
+ MIME-base64 standard. Otherwise the output conforms to :rfc:`3548`.
.. function:: a2b_qp(data, header=False)
@@ -168,7 +170,8 @@
.. seealso::
Module :mod:`base64`
- Support for base64 encoding used in MIME email messages.
+ Support for RFC compliant base64-style encoding in base 16, 32, 64,
+ and 85.
Module :mod:`binhex`
Support for the binhex format used on the Macintosh.