--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/bnf.rst	Mon Feb 22 12:46:36 2016 +0200
@@ -0,0 +1,52 @@
+.. -*- coding: utf-8; -*-
+.. include:: HEADER.rst
+
+=====
+ BNF
+=====
+
+What is BNF?
+============
+.. contents::
+   :local:
+
+BNF is an acronym for "Backus Naur Form". John Backus and Peter Naur introduced
+for the first time a formal notation to describe the syntax of a given language
+(ALGOL 60 programming language).
+
+See: :rfc:`2234`.
+
+BNF syntax
+==========
+
+The meta-symbols of BNF are:
+
+  ``::=``
+    Meaning "is defined as".
+  ``|``
+    Meaning "or".
+  ``<``,  ``>``
+    Angle brackets used to surround category names (some times skipped).
+  ``[``,  ``]``
+    Optional items are enclosed in.
+  ``{``,  ``}``
+    Repetitive items (zero or more times) are enclosed in.
+  ``"abc..."``
+    Terminals are enclosed in to distinguish them from meta-symbols.
+
+BNF in BNF
+==========
+::
+
+  syntax     ::=  { rule }
+  rule       ::=  identifier  "::="  expression
+  expression ::=  term { "|" term }
+  term       ::=  factor { factor }
+  factor     ::=  identifier |
+                  quoted_symbol |
+                  "("  expression  ")" |
+                  "["  expression  "]" |
+                  "{"  expression  "}"
+  identifier ::=  letter { letter | digit }
+  quoted_symbol ::= """ { any_character } """
+