Create a Custom Tab

Question

When I start a new Excel Web Add-in, by default the blank project has a MyAppName.xml file that declares the ribbon. The declaration sets a custom group and a custom control under the native Home Excel tab.

What I want is to create a separate tab for my Addin. In the file project itself, there are these code lines:

<!-- Use OfficeTab to extend an existing Tab. Use CustomTab to create a new tab. -->
<OfficeTab id="TabHome">

So I changed OfficeTab for CustomTab, but now I get the message in the error list:

The element 'CustomTab' in namespace 'http://schemas.microsoft.com/office/taskpaneappversionoverrides' has incomplete content. List of possible elements expected: 'Group, Label' in namespace 'http://schemas.microsoft.com/office/taskpaneappversionoverrides'.

Do you know how I can create a custom tab? What am I doing wrong?

I'm using: Microsoft Visual Studio Enterprise 2017 Version 15.2 (26430.12) Release VisualStudio.15.Release/15.2.0+26430.12

Thanks.