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+# Zisp S-Expression Syntax
+
+We use a BNF notation with the following rules:
+
+* Concatenation of expressions is implicit: `foo bar` means `foo`
+  followed by `bar`.
+
+* Expressions may be followed by `?`, `*`, `+`, `{N}`, or `{N,M}`,
+  which have the meanings they have in regular expressions.
+
+* The syntax is defined in terms of bytes, not characters.  Terminals
+  `'c'` and `"c"` refer to the ASCII value of the given character `c`.
+  Numbers are in decimal and refer to a byte with the given value.
+
+* The `~` prefix means NOT.  It only applies to rules that match one
+  byte, and negates them.  For example, `~( 'a' | 'b' )` matches any
+  byte other than 97 and 98.
+
+* Ranges of terminal values are expressed as `x...y` (inclusive).
+
+* There is no ambiguity, backtracking, or look-ahead beyond the byte
+  currently being matched.  Rules match left to right, depth-first,
+  and greedy.  As soon as the input matches the first terminal of a
+  rule, it must match that rule to the end.
+
+The last rule means that the BNF is very simple to translate to code.
+
+The parser consumes one `unit` from an input stream every time it's
+called; it returns the `datum` therein, or EOF.
+
+```
+
+
+```