Applied to a type or field?

The Remarks section states that this attribute can be "applied to types, properties, fields, methods, and method parameters", then explains some cases, but not the types nor the field ones.
It would be beneficial to explain both these cases too, as they are not obvious.

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#### Document Details

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* ID: 11dfc639-e939-8944-28d6-9c82b53b0676
* Version Independent ID: cf71b269-876f-c64d-72fb-23fc83a9b8c9
* Content: [CustomValidationAttribute Class (System.ComponentModel.DataAnnotations)](https://docs.microsoft.com/en-us/dotnet/api/system.componentmodel.dataannotations.customvalidationattribute?view=netframework-4.7.2#remarks)
* Content Source: [xml/System.ComponentModel.DataAnnotations/CustomValidationAttribute.xml](https://github.com/dotnet/dotnet-api-docs/blob/master/xml/System.ComponentModel.DataAnnotations/CustomValidationAttribute.xml)
* Product: **.net**
* GitHub Login: @dotnet-bot
* Microsoft Alias: **riande**

Open xml/System.ComponentModel.DataAnnotations/CustomValidationAttribute.xml and read the Remarks content for CustomValidationAttribute. Expand the explanation to cover how the attribute applies to types and fields, matching the existing discussion of other targets. Done means the generated Remarks documentation clearly explains both cases.

Scritto dal modello di indicizzazione a partire dal testo della issue.