This is the default tab because the <header> tag has a class of default-tab.

Notice how the algorithm walked up the hierarchy selecting each containing tab as well.

Another way to make a tab the default is to include tabz-enable in the class attribute of both the <header> and it's <section> tags.

You can also simulate a click on a tag by calling tagz.init(element) or tagz.init(selector) which is what this button does: