// Script that evaluates to a selector engine instance. The script is evaluated in the page context.
String createTagNameEngine = "{\n" +
  "  // Returns the first element matching given selector in the root's subtree.\n" +
  "  query(root, selector) {\n" +
  "    return root.querySelector(selector);\n" +
  "  },\n" +
  "  // Returns all elements matching given selector in the root's subtree.\n" +
  "  queryAll(root, selector) {\n" +
  "    return Array.from(root.querySelectorAll(selector));\n" +
  "  }\n" +
  "}";
// Register the engine. Selectors will be prefixed with "tag=".
playwright.selectors().register("tag", createTagNameEngine);
Browser browser = playwright.firefox().launch();
Page page = browser.newPage();
page.setContent("<div><button>Click me</button></div>");
// Use the selector prefixed with its name.
Locator button = page.locator("tag=button");
// Combine it with built-in locators.
page.locator("tag=div").getByText("Click me").click();
// Can use it in any methods supporting selectors.
int buttonCount = (int) page.locator("tag=button").count();
browser.close();