How to extend Workflow Editor

(function() {
    var Workflow = Synquery.ext.Workflow;
    var Activities = Workflow.Activities;
    var Activity = Activities.Activity;
    var util = Workflow.Utilities;
    
    // (1)
    Activities.PrintAndSendMailActivity = PrintAndSendMailActivity;

    // (2)
    function PrintAndSendMailActivity() {
        Activity.apply(this, arguments);
    };
    // (3)
    util.inherit(PrintAndSendMailActivity, Activity);
    
    // (4)
    PrintAndSendMailActivity.display = 'Print and Send mail';
    
    // (5)
    PrintAndSendMailActivity.explain = 'Outputs a voucher of this workflow with sending mail.';
    
    // (6)
    PrintAndSendMailActivity.prototype.action = function(data) {
        this.book.PrintForm();
        return Activity.prototype.action.apply(this, arguments);
    };
    
    // (7)
    PrintAndSendMailActivity.prototype.save = function(data) {
        var x = this.book;
        return Activity.prototype.save.apply(this, arguments).pipe(function() {
            var def = $.Deferred();
            x.top.BOOK({
                'title': 'Send Mail',
                'structure': [
                    ['to[]', '', [
                        ['email', 'Email', 'email', '', {'fill': true}, 90]
                    ], 100, {}, 10]
                ],
                'style': {'modal': true, 'editForm': true, 'noSearch': true},
                'table': false,
                'formButton': {
                    'send': function(x) {
                        var form = x.GetForm();
                        if(x.CheckForm())
                            return;
                        x.RemoveForm();
                        var param = {'subject': 'Action is executed', 'contents': 'Please check it.'};
                        param.to = form.to.email;
                        x.top.sendMail(param, function(info, err) {
                            if(err || !info['success'])
                                return def.reject(err);
                            def.resolve();
                        });
                }}
            }, x).ShowForm();
            return def.promise();
        });
    };
  
}).call();