Refactor code-style

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

lib/index.js

@@ -8,18 +8,22 @@ import {visit} from 'unist-util-visit'
  * Remove the `position` field from a tree.
  *
  * @template {Node} Tree
- * @param {Tree} node
- * The unist tree.
- * @param {boolean} [force=false]
- * If `force` is given (`boolean`, default: `false`), uses `delete` to remove
- * the field entirely, otherwise it’s set to `undefined`.
+ * Node type.
+ * @param {Tree} tree
+ * Tree to clean.
+ * @param {boolean | null | undefined} [force=false]
+ * Whether to use `delete` to remove `position` fields.
+ *
+ * The default is to set them to `undefined`.
  * @returns {Tree}
- * The given, modified, `node`.
+ * The given, modified, `tree`.
  */
-export function removePosition(node, force) {
- visit(node, remove)
+// To do: next major: return `void`.
+// To do: remove `force` shortcut, replace with options.
+export function removePosition(tree, force) {
+ visit(tree, remove)
 
- return node
+ return tree
 
  /**
  * @param {Node} node