Revise UPGRADING_v6.md

Signed-off-by: Jack Cherng <jfcherng@gmail.com>

Author: jfcherng

UPGRADING/UPGRADING_v6.md

@@ -7,39 +7,41 @@ If you only use the `DiffHelper` and built-in `Renderer`s,
 there is no breaking change for you so you do not have to do anything.
 
 
-### External Breaking Changes
+### Breaking Changes for Normal Users
 
-- The `Diff` class has been renamed to `Differ`.
-  It's easy to adapt to this by changing the class name.
+- The `Diff` class has been renamed as `Differ`.
+  It should be relatively easy to adapt to this by changing the class name.
 
-- The term `template` has been renamed to `renderer`. Some examples are:
+- The term `template` has been renamed as `renderer`. Some examples are:
 
   - Method `DiffHelper::getRenderersInfo()`
   - Method `DiffHelper::getAvailableRenderers()`
   - Constant `RendererConstant::RENDERER_TYPES`
   - Constant `AbstractRenderer::IS_TEXT_RENDERER`
 
 - Now a `Renderer` has a `render()` method, but a `Differ` does not.
+  (because it makes more sense saying a renderer would render something)
   If you use those classes by yourself, it should be written like below.
 
   ```php
   use Jfcherng\Diff\Differ;
   use Jfcherng\Diff\Factory\RendererFactory;
 
   $differ = new Differ(explode("\n", $old), explode("\n", $new), $diffOptions);
-  $renderer = RendererFactory::make($renderer, $rendererOptions);
-  $result = $renderer->render($differ); // <-- this has been changed
+  $renderer = RendererFactory::make($rendererName, $rendererOptions);
+  $result = $renderer->render($differ); // <-- this line has been changed
   ```
 
-- Add `RendererInterface::getResultForIdenticals()`.
-  `AbstractRenderer::getResultForIdenticals()` returns an empty string by default.
 
-- Remove the deprecated `AbstractRenderer::getIdenticalResult()`.
-  Use/implement the `AbstractRenderer::getResultForIdenticals()` instead.
+### Breaking Changes for Customized Renderer Developers
 
-
-### Internal Breaking Changes
+- Remove the deprecated `AbstractRenderer::getIdenticalResult()` and
+  add `RendererInterface::getResultForIdenticals()`. The returned value will be
+  directly used before actually starting to calculate diff if we find that the
+  two strings are the same. `AbstractRenderer::getResultForIdenticals()` 
+  returns an empty string by default.
 
 - Now a `Renderer` should implement `protected function renderWoker(Differ $differ): string`
-  rather than the previous `public function render(): string`. Note that `$this->diff` no longer
-  works in `Renderer`s as it is now injected as the parameter to `Renderer::renderWoker()`.
+  rather than the previous `public function render(): string`. Note that 
+  `$this->diff` no longer works in `Renderer`s as it is now injected as a 
+  parameter to `Renderer::renderWoker()`.