Refactor code-style

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

Author: wooorm

lib/index.js

@@ -1,10 +1,7 @@
 /**
  * @typedef {import('unist').Node} Node
  * @typedef {import('unist').Parent} Parent
- *
- * @typedef {string} Type
- * @typedef {Record<string, unknown>} Props
- * @typedef {import('unist-util-is').TestFunctionAnything} TestFunctionAnything
+ * @typedef {import('unist-util-is').Test} Test
  */
 
 import {convert} from 'unist-util-is'
@@ -17,24 +14,25 @@ import {convert} from 'unist-util-is'
  *   Parent node.
  * @param index
  *   Child of `parent`, or it’s index.
- * @param [test]
+ * @param test
  *   `unist-util-is`-compatible test.
  * @returns
+ *   Child of `parent` or `null`.
  *
  */
 export const findBefore =
   /**
    * @type {(
-   *  (<T extends Node>(node: Parent, index: Node|number, test: T['type']|Partial<T>|import('unist-util-is').TestFunctionPredicate<T>|Array<T['type']|Partial<T>|import('unist-util-is').TestFunctionPredicate<T>>) => T|null) &
-   *  ((node: Parent, index: Node|number, test?: null|undefined|Type|Props|TestFunctionAnything|Array<Type|Props|TestFunctionAnything>) => Node|null)
+   *  (<T extends Node>(node: Parent, index: Node | number, test: import('unist-util-is').PredicateTest<T>) => T | null) &
+   *  ((node: Parent, index: Node | number, test?: Test) => Node | null)
    * )}
    */
   (
     /**
      * @param {Parent} parent
-     * @param {Node|number} index
-     * @param {null|undefined|Type|Props|TestFunctionAnything|Array<Type|Props|TestFunctionAnything>} [test]
-     * @returns {Node|null}
+     * @param {Node | number} index
+     * @param {Test} [test]
+     * @returns {Node | null}
      */
     function (parent, index, test) {
       const is = convert(test)