Missing documentation for IModelValidatorProvider

From the stackoverflow post: https://stackoverflow.com/questions/57777755/how-to-implement-custom-model-validator-in-net-core

Is `IModelValidatorProvider `something that is no longer recommended? I didn't find a mention to this type of validation in the doc.

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#### Document Details

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* ID: 0156ffc3-47ac-d5da-fbc2-9ff5018b071b
* Version Independent ID: 615db388-a244-41f7-21b5-a4085d9ed479
* Content: [Model validation in ASP.NET Core MVC](https://docs.microsoft.com/en-us/aspnet/core/mvc/models/validation?view=aspnetcore-3.1)
* Content Source: [aspnetcore/mvc/models/validation.md](https://github.com/dotnet/AspNetCore.Docs/blob/master/aspnetcore/mvc/models/validation.md)
* Product: **aspnet-core**
* Technology: **aspnetcore-mvc**
* GitHub Login: @Rick-Anderson
* Microsoft Alias: **riande**