This document describes the types of keys available.
Keys can be one of three types, selected by choosing the appropriate constructor:
The key is defined to be a descriptor,
i.e. an object derived from TDesC. In practice, a descriptor
key within an array element is one of the types: TPtrC, TPtr, TBufC or TBuf (but
not an HBufC).
For a Unicode build, they are defined
as TDesc16, TPtrC16, TPtr16, TBufC16 and TBuf16 respectively,
while for a non-Unicode build, they are defined as TDesc8 TPtrC8, TPtr8, TBufC8 and TBuf8 respectively.
The key is defined to be of type TText.
For a Unicode build, TText is defined as TText16 while
for a non-Unicode build, it is defined as TText8.
The key is defined to be of type: TInt, TInt8, TInt16, TInt32, TInt64, TUint, TUint8, TUint16 or TUint32.