Issue #13748: Raw bytes literals can now be written with the `rb` prefix as well as `br`.
diff --git a/Doc/reference/lexical_analysis.rst b/Doc/reference/lexical_analysis.rst
index 5900daa..c20c47e 100644
--- a/Doc/reference/lexical_analysis.rst
+++ b/Doc/reference/lexical_analysis.rst
@@ -412,7 +412,7 @@
 
 .. productionlist::
    bytesliteral: `bytesprefix`(`shortbytes` | `longbytes`)
-   bytesprefix: "b" | "B" | "br" | "Br" | "bR" | "BR"
+   bytesprefix: "b" | "B" | "br" | "Br" | "bR" | "BR" | "rb" | "rB" | "Rb" | "RB"
    shortbytes: "'" `shortbytesitem`* "'" | '"' `shortbytesitem`* '"'
    longbytes: "'''" `longbytesitem`* "'''" | '"""' `longbytesitem`* '"""'
    shortbytesitem: `shortbyteschar` | `bytesescapeseq`
@@ -446,6 +446,10 @@
 literal characters.  As a result, in string literals, ``'\U'`` and ``'\u'``
 escapes in raw strings are not treated specially.
 
+   .. versionadded:: 3.3
+      The ``'rb'`` prefix of raw bytes literals has been added as a synonym
+      of ``'br'``.
+
 In triple-quoted strings, unescaped newlines and quotes are allowed (and are
 retained), except that three unescaped quotes in a row terminate the string.  (A
 "quote" is the character used to open the string, i.e. either ``'`` or ``"``.)