Improve code documentation

index.js

@@ -11,42 +11,47 @@
  * [Hermes Parser]
  * https://github.com/facebook/hermes/blob/main/tools/hermes-parser/js/babel-plugin-syntax-hermes-parser
  *
- * [Other]
+ * [Ponyfills]
  * https://babeljs.io/docs/en/babel-plugin-transform-runtime
  */
 
 /**
- * Notes
+ * [Notes]
  *
  * Presets are run in the reverse order they are defined.
  * Plugins are run in the order they are defined below,
  * but they are run *before* presets.
  */
 
 /**
- * 1. https://babeljs.io/docs/babel-generator#:~:text=importAttributesKeyword
+ * 1. Will be set as default from Babel 8.
  *
  * 2. Ensure all helpers are imported instead of inlined.
  *    See https://github.com/babel/babel/issues/9297#issuecomment-453750049
+ *
+ * 3. https://babeljs.io/docs/babel-generator#:~:text=importAttributesKeyword
+ *
+ * 4. https://babeljs.io/docs/babel-preset-flow#allowdeclarefields
+ *    See `Regression: Flow void class properties` test.
  */
 
 module.exports = (context, options = {}) => {
   let { parser = 'babel', ...envOptions } = options;
 
   let configOpts = {
     generatorOpts: {
-      importAttributesKeyword: 'with', // 1
+      importAttributesKeyword: 'with', // 3
     },
   };
 
   let envOpts = {
-    bugfixes: true,
+    bugfixes: true, // 1
     ...envOptions,
   };
 
   let reactOpts = {
-    useSpread: true,
-    runtime: 'automatic',
+    useSpread: true, // 1
+    runtime: 'automatic', // 1
   };
 
   let runtimeOpts = {
@@ -56,10 +61,14 @@ module.exports = (context, options = {}) => {
     version: '7.26.0', // 2
   };
 
+  let flowOpts = {
+    // allowDeclareFields: true, // 4
+  };
+
   let presets = [
     ['@babel/preset-env', envOpts],
     ['@babel/preset-react', reactOpts],
-    '@babel/preset-flow',
+    ['@babel/preset-flow', flowOpts],
   ];
 
   let plugins = [