While it is possible to do some customization of onSelectDay with current onSelect callback, the resulting range selection cannot be customized. One can think of use cases where a different implementation might be more appropriate. In many travel booking sites it is possible to modify one end of the selection range while keeping the other end unchanged. I recommend to keep the existing implementation as a default but allow it to be overwritten.
While it is possible to do some customization of onSelectDay with current onSelect callback, the resulting range selection cannot be customized. One can think of use cases where a different implementation might be more appropriate. In many travel booking sites it is possible to modify one end of the selection range while keeping the other end unchanged. I recommend to keep the existing implementation as a default but allow it to be overwritten.