stringByAppendingFormat: unimplemented

Here is a possible implementation:

@@@javascript /*

Creates a new <objj>CPString</objj> from the concatenation of the receiver and the specified format and arguments in the manner of stringWithFormat:.
@param format the format, printf-style to append to the receiver,
@return the new string

*/ - (CPString)stringByAppendingFormat:(CPString)format, ... {

if (!format)
    [CPException raise:CPInvalidArgumentException
                reason:"stringByAppendingFormat: the format can't be 'nil'"];

return self + sprintf.apply(this, Array.prototype.slice.call(arguments, 2));

}