---
id: extensibility
title: "Extensibility"
---

<!-- TOC -->

## Custom selector engines

Playwright supports custom selector engines, registered with [`method: Selectors.register`].

Selector engine should have the following properties:
- `create` function to create a relative selector from `root` (root is either a `Document`, `ShadowRoot` or `Element`)
  to a `target` element.
- `query` function to query first element matching `selector` relative to the `root`.
- `queryAll` function to query all elements matching `selector` relative to the `root`.

By default the engine is run directly in the frame's JavaScript context and, for example, can call an
application-defined function. To isolate the engine from any JavaScript in the frame, but leave access to the DOM,
register the engine with `{contentScript: true}` option. Content script engine is safer because it is protected from any
tampering with the global objects, for example altering `Node.prototype` methods. All built-in selector engines run as
content scripts. Note that running as a content script is not guaranteed when the engine is used together with other
custom engines.

An example of registering selector engine that queries elements based on a tag name:

```js
// Must be a function that evaluates to a selector engine instance.
const createTagNameEngine = () => ({
  // Returns the first element matching given selector in the root's subtree.
  query(root, selector) {
    return root.querySelector(selector);
  },

  // Returns all elements matching given selector in the root's subtree.
  queryAll(root, selector) {
    return Array.from(root.querySelectorAll(selector));
  }
});

// Register the engine. Selectors will be prefixed with "tag=".
await selectors.register('tag', createTagNameEngine);

// Now we can use 'tag=' selectors.
const button = await page.$('tag=button');

// We can combine it with other selector engines using `>>` combinator.
await page.click('tag=div >> span >> "Click me"');

// We can use it in any methods supporting selectors.
const buttonCount = await page.$$eval('tag=button', buttons => buttons.length);
```

```python async
tag_selector = """
    // Must evaluate to a selector engine instance.
    {
      // Returns the first element matching given selector in the root's subtree.
      query(root, selector) {
        return root.querySelector(selector);
      },

      // Returns all elements matching given selector in the root's subtree.
      queryAll(root, selector) {
        return Array.from(root.querySelectorAll(selector));
      }
    }"""

# register the engine. selectors will be prefixed with "tag=".
await playwright.selectors.register("tag", tag_selector)

# now we can use "tag=" selectors.
button = await page.query_selector("tag=button")

# we can combine it with other selector engines using `>>` combinator.
await page.click("tag=div >> span >> "click me"")

# we can use it in any methods supporting selectors.
button_count = await page.eval_on_selector_all("tag=button", buttons => buttons.length)
```

```python sync
tag_selector = """
    // Must evaluate to a selector engine instance.
    {
      // Returns the first element matching given selector in the root's subtree.
      query(root, selector) {
        return root.querySelector(selector);
      },

      // Returns all elements matching given selector in the root's subtree.
      queryAll(root, selector) {
        return Array.from(root.querySelectorAll(selector));
      }
    }"""

# register the engine. selectors will be prefixed with "tag=".
playwright.selectors.register("tag", tag_selector)

# now we can use "tag=" selectors.
button = page.query_selector("tag=button")

# we can combine it with other selector engines using `>>` combinator.
page.click("tag=div >> span >> "click me"")

# we can use it in any methods supporting selectors.
button_count = page.eval_on_selector_all("tag=button", buttons => buttons.length)
```