[libvirt] [question] Why doesn't virsh command support an optional parameter

hi guys, It's hard for me to understand why doesn't virsh command support an optional parameter because I think omitting a parameter and offering a default value sometimes is quite convenient. For example: $ virsh shutdown guest --mode acpi The option --mode only accept string "acpi", "agent", "initctl" and "signal", assuming that "acpi" is the most frequently used parameter when --mode is specified, why not just using $ virsh shutdown guest --mode acpi instead. Maybe this example is not very precise, but what I mean is if there is an option which only accepts several candidate values and one of the value is always used when it is specified, then we can make it the default parameter of this option. This would be convenient and save some typing. Of course, this can also result in ambiguity to people who is not familiar with the command. But with the help, it won't trap one very long, will it? So, why doesn't virsh support this and what do you think of adding this feature? Thanks Zhang Xiaohe