Called by the Agentry to get the value for the specified string. 
      Syntax
         
         
            - 
            (
            NSString *
            ) 
            
               model
            
            : 
            (
            id< SMPOpenUIFieldModel >
            ) 
            model 
            
               wantsExtensionString
            
            : 
            (
            NSString *
            ) 
            stringName
         
      
      Parameters
         
         
            - 
               model – 
               the model
            
 
            - 
               stringName – 
               The string that Agentry is requesting
            
 
         
       
      Returns
         The value the extension determines based on the specified key
      Remarks
         
         In the definitions, there are specified keys. The string passed in is a key, the value is returned from the extension.