Added Parser AST format specification.

AST.md

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+JSX extensions to Mozilla AST Format
+====================================
+
+JSX extends ECMAScript [Mozilla AST format](https://developer.mozilla.org/en-US/docs/Mozilla/Projects/SpiderMonkey/Parser_API) with following node types:
+
+JSX Names
+---------
+
+__JSX Identifier subtype__
+
+```
+interface XJSIdentifier <: Identifier {
+    type: "XJSIdentifier";
+}
+```
+
+__Namespaced names__
+
+Property-like namespace syntax (tag names only):
+
+```
+interface XJSMemberExpression <: Expression, Pattern {
+    type: "XJSMemberExpression";
+    object: XJSMemberExpression | XJSIdentifier,
+    property: XJSIdentifier
+}
+```
+
+XML-based namespace syntax:
+
+```
+interface XJSNamespacedName <: Expression, Pattern {
+    type: "XJSNamespacedName";
+    namespace: XJSIdentifier,
+    name: XJSIdentifier
+}
+```
+
+JSX Expression Container
+------------------------
+
+JSX adds empty "expression" type in order to allow comments in JSX text:
+
+```
+interface XJSEmptyExpression <: Node {
+    type: "XJSEmptyExpression"
+}
+```
+
+Any expression used as attribute value or inside JSX text should is wrapped into expression container:
+
+```
+interface XJSExpressionContainer <: Node {
+    type: "XJSExpressionContainer",
+    expression: Expression | XJSEmptyExpression;
+}
+```
+
+JSX Boundary Tags
+-----------------
+
+Any JSX element is bounded by tags &mdash; either self-closing or both opening and closing elements:
+
+```
+interface XJSBoundaryElement <: Node {
+    name: XJSIdentifier | XJSMemberExpression | XJSNamespacedName;
+}
+
+interface XJSOpeningElement <: XJSBoundaryElement {
+    type: "XJSOpeningElement",
+    attributes: [ XJSAttribute | XJSSpreadAttribute ],
+    selfClosing: boolean;
+}
+
+interface XJSClosingElement <: XJSBoundaryElement {
+    type: "XJSClosingElement"
+}
+```
+
+JSX Attributes
+--------------
+
+Opening element ("tag") may contain attributes:
+
+```
+interface XJSAttribute <: Node {
+    type: "XJSAttribute",
+    name: XJSIdentifier | XJSNamespacedName,
+    value: Literal | XJSExpressionContainer | XJSElement | null
+}
+
+// This is already used by ES6 parsers, but not included
+// in Mozilla's spec yet.
+interface SpreadElement <: Pattern {
+    type: "SpreadElement";
+    argument: Expression;
+}
+
+interface XJSSpreadAttribute <: SpreadElement {
+    type: "XJSSpreadAttribute";
+}
+```
+
+JSX Element
+-----------
+
+Finally, JSX element itself consists of opening element, list of children and optional closing element:
+
+```
+interface XJSElement <: Expression {
+    type: "XJSElement",
+    openingElement: XJSOpeningElement,
+    children: [ Literal | XJSExpressionContainer | XJSElement ],
+    closingElement: XJSClosingElement | null
+}
+```
+
+Tools that work with JSX AST
+----------------------------
+
+* Parsers:
+  - [acorn-jsx](https://github.com/RReverser/acorn-jsx): A fork of acorn.
+  - [esprima-fb](https://github.com/facebook/esprima): A fork of esprima.
+* Traversal: [estraverse-fb](https://github.com/RReverser/estraverse-fb).
+* Node creation and declarative traversal: [ast-types](https://github.com/benjamn/ast-types)
+* Transpiling to ECMAScript AST: [jsx-transpiler](https://github.com/RReverser/jsx-transpiler)
+
+License
+-------
+
+Copyright (c) 2014, Facebook, Inc.
+All rights reserved.
+
+This work is licensed under a [Creative Commons Attribution 4.0
+International License](http://creativecommons.org/licenses/by/4.0/).