Allows the delegate to validate the tokens to be added to the receiver at a given index.
- macOS 10.4+
The token field cell that sent the message.
An array of tokens to be inserted in the receiver at
The index of the receiver in which the array of tokens to be validated (
tokens) will be inserted.
An array of validated tokens.
The delegate can return the array unchanged or return a modified array of tokens. To reject the add completely, return an empty array. Returning
nil causes an error.