| A group of args, of which either zero or one may be set, but not more.    Members:
        subargsa list [(argname, arg), ...] of Arg instances.argnameis used to identify the corresponding arg in
            error messages.  (The name of the corresponding keyword
            args is determined internally by each arg.) 
        
            | Methods |  |  
        | __call__ __init__
 
 |  
            |  | __call__ |  
        | 
__call__ ( self,  keyw )
 
        
            | Exceptions |  |  
        | Errors.OptionError('Arguments %s and %s cannot both be specified' %( foundargname, argname, ) ) 
 |  |  
            |  | __init__ |  
        | 
__init__ ( self,  *subargs )
 |  |