Specification: need to elaborate postfix expression definition

Dart Language specification, 4-th Edition (December, 2015) "16.31 Postfix Expressions":

> A postfix expression is either a primary expression, a function, method or getter invocation, or an invocation of a postfix operator on an expression e.
> ...
> Execution of a postfix expression of the form C.v ++ is equivalent to executing
> ()fvar r = C.v; C.v = r + 1; return rg().
> The static type of such an expression is the static type of C.v.
> Execution of a postfix expression of the form e1.v++ is equivalent to executing
> (x)fvar r = x.v; x.v = r + 1; return rg(e1).
> The static type of such an expression is the static type of e1.v.
> No any mention about the difference between C and e1. Clarification should be added that C is a type literal and e1 is an expression.

The same is true for C.v-- and e1.v-- defined in the same chapter of the spec

Start with Dart Language Specification, 4th Edition, section 16.31, “Postfix Expressions,” and review the definitions and execution rules for C.v++ and e1.v++. Clarify that C is a type literal while e1 is an expression, and apply the same distinction to C.v-- and e1.v--; done means the specification explicitly explains both forms.

Written by the indexing model from the issue text.