[question] mousebind -- button chords

[dnlo]

Thank you for this library, it's real nice, made things so much easier

Mousebind docs say mouse buttons can be modifiers, so mouse chords should work.

But running this code:

package main

import (
    "log"

    "github.com/BurntSushi/xgbutil"
    "github.com/BurntSushi/xgbutil/mousebind"
    "github.com/BurntSushi/xgbutil/xevent"
)

func main() {
    X, err := xgbutil.NewConn()
    if err != nil {
        log.Fatal(err)
    }
    mousebind.Initialize(X)

    cb1 := mousebind.ButtonPressFun(
        func(X *xgbutil.XUtil, e xevent.ButtonPressEvent) {
            log.Println("Button press!")
        })

    err = cb1.Connect(X, X.RootWin(), "button3-1", false, true)
    if err != nil {
        log.Println(err)
    }

    xevent.Main(X)
}

Produces this error:

Could not bind 'button3-1' because: 
BadValue {NiceName: Value, Sequence: 5, BadValue: 1024, MinorOpcode: 0, MajorOpcode: 28}

Any kind of help for solving this would be much appreciated. Thank you again for all your great work