SetCapacity is the protected write implementation of the Capacity property. 

In TAbstractNamedVariants, SetCapacity does nothing, because TAbstractNamedVariants does not implement support for preallocating memory to hold name/Variant pairs that have not been added to the list. Descendant classes that provide support for allocating memory before adding items to the list override SetCapacity to reallocate the memory used to hold list items. 

Capacity 

GetCapacity