ExtJS: add button to htmleditor

I am using ExtJS and I have a htmleditor in my form. I would like to add a custom button to that element (for example after all other buttons like alignments, font weights, ...). This button should basically insert a standard template in the htmlfield. Being this template html, the behaviour of the button should be like this

• Switch to HTML mode (like when pressing Source button)
• Insert something
• Switch back to WYSIWYG mode (like when pressing the Source button again)

Ext.ns('Ext.ux.form.HtmlEditor');

Ext.ux.form.HtmlEditor.HR = Ext.extend(Ext.util.Observable, {
    init: function(cmp){
        this.cmp = cmp;
        this.cmp.on('render', this.onRender, this);
    },
    onRender: function(){
        this.cmp.getToolbar().addButton([{
            iconCls: 'x-edit-custom', //your iconCls here
            handler: function(){
                this.cmp.insertAtCursor('<hr>');
            },
            scope: this,
            tooltip: 'horizontal ruler',
            overflowText: 'horizontal ruler'
        }]);
    }
});

var w = new Ext.Window({
    width: 550,
    layout: 'fit',
    items: [{
        xtype: 'htmleditor',
        plugins: [new Ext.ux.form.HtmlEditor.HR()]
    }]
});
w.show();

But I really recommend you to see the project HtmlEditor.Plugins at google code. There you can find a lot more about adding custom buttons, for instance, how to enable/disable the buttons when something is selected, put separators, etc.
https://docs.google.com/file/d/0B5nZNPW48dpFb0hJVmpVUEphZGc/edit?usp=sharing