Can not specify a flags 2+ times

[kovetskiy]

Hello, I have this docopt help-usage:

package main

import (
    "fmt"

    "github.com/docopt/docopt-go"
)

const (
    usage = `
Tool 1.0

Usage:
    tool [options] -P (-a|-r) <package>
    tool [options] -S (-a|-r) <config>

Options:
    -P --package     Package mode
        -a --add     add package
        -r --remove  remove package
    -S --service     Service mode
        -a --add     add service
        -r --remove  remove service
`
)

func main() {
    args, err := docopt.Parse(usage, nil, true, "tool 1.0", true, false)
    if err != nil {
        panic(err)
    }
    fmt.Printf("XXXXXX a.go:32: args: %#v\n", blah)
}

But when I run docopt.Parse with this usage, I got:

panic: -a is specified ambiguously 2 times

goroutine 1 [running]:
main.main()
        /home/vxw/a.go:30 +0x10a

So, this is really correct behaviour? Why usage can't have a repetable flags?