update: readme

README.md

@@ -170,10 +170,10 @@ Share & find custom scripts here: https://github.com/windingwind/zotero-actions-
 
 You can use the following variables in the script:
 
-- `item`: The target item. Might be `undefined` if the action is triggered by an event that doesn't have a target item, e.g. shortcut in the Zotero client without selecting an item. (Not available in `programStartup`, `mainWindowLoad`, and `mainWindowUnload` event)
+- `item`: The target item. Might be `null` if the action is triggered by an event that doesn't have a target item, e.g. shortcut in the Zotero client without selecting an item. (Not available in `programStartup`, `mainWindowLoad`, and `mainWindowUnload` event)
 
 <details style="text-indent: 4em">
-<summary>Examples with item</summary>
+<summary>Examples with `item`</summary>
 
 - Get the title of the item: `item.getField('title')`. More details of the available fields can be found in [Zotero:item fields](https://api.zotero.org/itemFields?pprint=1)
 - Get the tags of the item: `item.getTags().map(tag => tag.tag)`
@@ -182,10 +182,30 @@ You can use the following variables in the script:
 
 </details>
 
+- `items`: The target items[] array. Only available in menu/shortcut-triggered actions, otherwise it's `null`.
+
+<details style="text-indent: 4em">
+<summary>Examples with `items`</summary>
+
+When selecting multiple items in the library, the action will be triggered for each item. You can use the `items` variable to get the selected items array and avoid duplicate operations.
+
+```js
+if (!items && item) {
+  // Disable the action if it's triggered for a single item to avoid duplicate operations
+  return;
+}
+
+if (items?.length > 0) {
+  // Do something with the selected items
+}
+```
+
+</details>
+
 - `require`: The `require` function to import global variables. Use `const window = require('window')` to import the `window` variable.
 
 <details style="text-indent: 4em">
-<summary>Examples with require</summary>
+<summary>Examples with `require`</summary>
 
 - Get selected items: `const selectedItems = require('ZoteroPane').getSelectedItems()`
 - Get the item of current tab: