in src/XDM.ts [213:223]
    constructor(postToWindow: Window, targetOrigin?: string) {
        this.postToWindow = postToWindow;
        this.targetOrigin = targetOrigin;
        this.registry = new XDMObjectRegistry();
        this.channelId = nextChannelId++;
        if (!this.targetOrigin) {
            this.handshakeToken = newFingerprint();
        }
    }