[Documentation] Custom selector engines before page is created

[Exoow]

The documentation (both in code and https://playwright.dev/dotnet/docs/extensibility) states:
Selectors must be registered before creating the page.

However the code below works, in a TestClass inheriting from PageTest.
Isn't the page already created when entering this method, given that actions are performed on it?

[TestInitialize]
public async Task InitializeTest()
{
    await RegisterCustomSelectors(); // register here
    await Page.GotoAsync("/");
    await Page.Locator("myengine=test").FillAsync("hi"); // this works!
}

[Exoow]

I found the caveat though: when running more than 1 test, Playwright throws an exception because the selector is already registered...

[mxschmitt]

Yes, there is currently no great way of adding a custom selector engine in .NET. TestInitialize is too late.

What kind of selector engine are you creating? We learned that for most users the integrated selector engines are enough.

[Exoow]

In TestInitialize works after adding a try/catch so it won't fail from the second test onwards.

We have tests running against Microsoft Dynamics, and it's easiest to select components by data-dyn-role or data-dyn-controlname attributes.
So instead of css=[data-dyn-controlname=something] I can write ddc=something.

An alternative could be to write extension methods on IPage and ILocator for this, but I like the brevity of the custom selectors.