Refactor code-style

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

Author: wooorm

lib/index.js

@@ -4,15 +4,31 @@
  * @typedef {Root|Content} Node
  *
  * @typedef Options
- * @property {boolean} [allowDashes=false]
- * @property {boolean} [allowApostrophes=false]
+ *   Configuration.
+ * @property {boolean | null | undefined} [allowDashes=false]
+ *   Do not strip hyphens (`-`).
+ *
+ *   The default is to remove the hyphen-minus character.
+ * @property {boolean | null | undefined} [allowApostrophes=false]
+ *   Do not strip apostrophes (`'`).
+ *
+ *   The default is to remove apostrophes.
  */
 
 import {toString} from 'nlcst-to-string'
 
 /**
- * @param {string|Node|Array<Content>} node
- * @param {Options} [options={}]
+ * Normalize a word for easier comparison.
+ *
+ * Always normalizes smart apostrophes (`’`) to straight apostrophes (`'`) and
+ * lowercases alphabetical characters (`[A-Z]`).
+ *
+ * @param {string | Node | Array<Content>} node
+ *   Word.
+ * @param {Options | null | undefined} [options]
+ *   Configuration.
+ * @returns {string}
+ *   Normalized word.
  */
 export function normalize(node, options) {
   let value = (typeof node === 'string' ? node : toString(node))