explainer § Why: Stub other justifications

See #8.

Author: js-choi

README.md

@@ -72,21 +72,30 @@ is equivalent to `a->(createFn())`.
 There are **no other special rules**.
 
 ## Why a bind-`this` operator
+
+### `call` and `bind` are very common and should be easier
 [`Function.prototype.bind`][call] and [`Function.prototype.call`][bind]
-are very common in **object-oriented JavaScript** code.
-They are useful methods that allows us to apply functions to any object,
+are very common in **object-oriented JavaScript** code;
+they could even be considered core parts of its design.
+
+[TODO]
+
+[bind]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind
+[call]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/call
+
+### Tree-shakable methods should be easier
+They allow developers to apply functions to any object,
 binding their first arguments to the `this` bindings within those functions,
 no matter the current object environment.
 `bind` and `call` allow us to **extend** an **object** with a function
 as if that function were **its own method**.
 They serve as an important link between
 the **object-oriented** and **functional** styles in JavaScript.
 
-[bind]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/bind
-[call]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Function/call
+[TODO]
 
-Why then would we need an operator that does the same thing?
-Because `bind` and `call` are vulnerable to **global mutation**.
+### Protection against global mutation should be easier
+`Function.prototype.bind` and `call` are vulnerable to **global mutation**.
 
 For example, when we run our code in an untrusted environment,
 an adversary may mutate global prototype objects