Merge pull request #3301 from jmm/ast-updates

Update AST spec

doc/ast/spec.md

@@ -141,7 +141,7 @@ interface Position {
 # Identifier
 
 ```js
-interface Identifier <: Node, Expression, Pattern {
+interface Identifier <: Expression, Pattern {
   type: "Identifier";
   name: string;
 }
@@ -151,6 +151,12 @@ An identifier. Note that an identifier may be an expression or a destructuring p
 
 # Literals
 
+```js
+interface Literal <: Expression { }
+```
+
+A literal token. May or may not represent an expression.
+
 ## RegExpLiteral
 
 ```js
@@ -929,6 +935,10 @@ interface TemplateElement <: Node {
 
 # Patterns
 
+```js
+interface Pattern <: Node { }
+```
+
 ## ObjectPattern
 
 ```js