export the option flag as new flag to sub command, so that this new flag can be pased as the
the option flag of parent command. this member function aims at avoidind flag conflict between
the command and its sub command, after using passThrough on this command.
this function would be automatically call Command.passThrough.
the flag must be the flag of one of the command's option or negate option.
remeber that when parsing the new flag, the option's new flag is prior to the negate option ones.
when parsing command line option flags, imported flag is prior to exported one, and the export one is
prior to the ordinary pass-through option flag.
isNegate decide whether export negate option or non-negate one, default: false
export the option flag as new flag to sub command, so that this new flag can be pased as the the option flag of parent command. this member function aims at avoidind flag conflict between the command and its sub command, after using passThrough on this command. this function would be automatically call Command.passThrough. the flag must be the flag of one of the command's option or negate option. remeber that when parsing the new flag, the option's new flag is prior to the negate option ones. when parsing command line option flags, imported flag is prior to exported one, and the export one is prior to the ordinary pass-through option flag. isNegate decide whether export negate option or non-negate one, default: false