public Version append(int number, String label) {
        validateNumber(number);
        return appendNumber(number, label);
    }
public Version append ( int number , String label ) { validateNumber ( number ) ; return appendNumber ( number , label ) ; }
Adds a new version number.

@param number version number (not negative).
@param label version number label (optional).
@return version descriptor.
@throws IllegalArgumentException if version number is illegal.

@since v1.1.0