Where does square icon come from?

[wetfeet]

I looked through the Icon Guide.

It says that:

• Font-Awesome starts with fa-
• Ionicons starts with ion-
• Material Icons starts with md-

Then I wonder where does this square icon used in the tabbar project template come from? Is there another set of built-in special icons?

<ons-tab page="page1.html" label="Page 1" icon="square" active></ons-tab>
                                                ^^^^^^

[misterjunio]

@wetfeet by inspecting the classes you can see that no prefix defaults to fa-