What does Dictionary<TKey,TValue>.EnsureCapacity(Int32) Method do?

Does it allocate space or just check to see if the space is currently allocatable? In bytes or element count?

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* ID: c24739cd-50ff-e3b1-a5b7-5e43fea977b0
* Version Independent ID: 39331194-8f05-25b9-88bb-5f77a0c53e95
* Content: [Dictionary<TKey,TValue>.EnsureCapacity(Int32) Method (System.Collections.Generic)](https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.dictionary-2.ensurecapacity?view=netcore-2.1&viewFallbackFrom=netframework-4.7.2)
* Content Source: [xml/System.Collections.Generic/Dictionary`2.xml](https://github.com/dotnet/dotnet-api-docs/blob/master/xml/System.Collections.Generic/Dictionary`2.xml)
* Product: **dotnet-api**
* GitHub Login: @dotnet-bot
* Microsoft Alias: **dotnetcontent**

Start with xml/System.Collections.Generic/Dictionary`2.xml and the linked Dictionary.EnsureCapacity(Int32) API page. Confirm whether the method allocates capacity or only checks availability, and whether its argument refers to bytes or elements. Done means the API documentation answers both questions clearly.

索引モデルが issue の本文から書いたものです。