So, the following will work:
```
page.frameLocator('iframe').locator('span').or(page.frameLoactor('iframe').locator('div'))
```
The following will not work, because frame locators are not exactly the
same:
```
page.frameLocator('#iframe1').locator('span').or(page.frameLoactor('#iframe2').locator('div'))
```
Also improve the error message to be more readable and include the
locator.
Fixes#23697.
