Refactor code-style

*   Add more docs to JSDoc
*   Add support for `null` in input of API types

index.js

@@ -1,6 +1,7 @@
 /**
  * @typedef {import('mdast-util-from-markdown').Extension} FromMarkdownExtension
  * @typedef {import('mdast-util-to-markdown').Options} ToMarkdownExtension
+ *
  * @typedef {import('mdast-util-mdx-expression').MdxFlowExpression} MdxFlowExpression
  * @typedef {import('mdast-util-mdx-expression').MdxTextExpression} MdxTextExpression
  * @typedef {import('mdast-util-mdxjs-esm').MdxjsEsm} MdxjsEsm
@@ -9,7 +10,6 @@
  * @typedef {import('mdast-util-mdx-jsx').MdxJsxExpressionAttribute} MdxJsxExpressionAttribute
  * @typedef {import('mdast-util-mdx-jsx').MdxJsxFlowElement} MdxJsxFlowElement
  * @typedef {import('mdast-util-mdx-jsx').MdxJsxTextElement} MdxJsxTextElement
- *
  * @typedef {import('mdast-util-mdx-jsx').ToMarkdownOptions} ToMarkdownOptions
  */
 
@@ -21,15 +21,29 @@ import {mdxJsxFromMarkdown, mdxJsxToMarkdown} from 'mdast-util-mdx-jsx'
 import {mdxjsEsmFromMarkdown, mdxjsEsmToMarkdown} from 'mdast-util-mdxjs-esm'
 
 /**
- * @return {Array<FromMarkdownExtension>}
+ * Create an extension for `mdast-util-from-markdown` to enable MDX (ESM, JSX,
+ * expressions).
+ *
+ * @returns {Array<FromMarkdownExtension>}
+ *   Extension for `mdast-util-from-markdown` to enable MDX (ESM, JSX,
+ *   expressions).
+ *
+ *   When using the syntax extensions with `addResult`, ESM and expression
+ *   nodes will have `data.estree` fields set to ESTree `Program` node.
  */
 export function mdxFromMarkdown() {
   return [mdxExpressionFromMarkdown, mdxJsxFromMarkdown(), mdxjsEsmFromMarkdown]
 }
 
 /**
- * @param {ToMarkdownOptions} [options]
- * @return {ToMarkdownExtension}
+ * Create an extension for `mdast-util-to-markdown` to enable MDX (ESM, JSX,
+ * expressions).
+ *
+ * @param {ToMarkdownOptions | null | undefined} [options]
+ *   Configuration.
+ * @returns {ToMarkdownExtension}
+ *   Extension for `mdast-util-to-markdown` to enable MDX (ESM, JSX,
+ *   expressions).
  */
 export function mdxToMarkdown(options) {
   return {

package.json

@@ -36,15 +36,15 @@
     "index.js"
   ],
   "dependencies": {
+    "mdast-util-from-markdown": "^1.0.0",
     "mdast-util-mdx-expression": "^1.0.0",
     "mdast-util-mdx-jsx": "^2.0.0",
-    "mdast-util-mdxjs-esm": "^1.0.0"
+    "mdast-util-mdxjs-esm": "^1.0.0",
+    "mdast-util-to-markdown": "^1.0.0"
   },
   "devDependencies": {
     "@types/tape": "^4.0.0",
     "c8": "^7.0.0",
-    "mdast-util-from-markdown": "^1.0.0",
-    "mdast-util-to-markdown": "^1.0.0",
     "micromark-extension-mdx": "^1.0.0",
     "micromark-extension-mdxjs": "^1.0.0",
     "prettier": "^2.0.0",