Detail about when capacity is increased

There's no detail explaining what happens when the internal array is resized - as I understand it, if the array isn't big enough, it creates a new array which is twice the size of the current one and copies the data. Although this is an implementation detail, I think it's interesting to note here, as it implies that using capacities that are powers of two would be more memory efficient than an arbitrary value.

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* Content: [List<T>.Capacity Property (System.Collections.Generic)](https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.list-1.capacity?view=netframework-4.7.2#System_Collections_Generic_List_1_Capacity)
* Content Source: [xml/System.Collections.Generic/List`1.xml](https://github.com/dotnet/dotnet-api-docs/blob/master/xml/System.Collections.Generic/List`1.xml)
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