@subsection Tab Group Element

@deftp {Web Component for VEvent} TabGroupElement
@wcindex <tab-group>
@wcindex tab-group
@code{<tab-group>}

A group of tabs, where only one can be visible at a time.

@c TODO which form does the HTML document have? For CSS purposes

Each tab consists of two parts, a label which is used for selecting
it, and a tab-element, which contains the actual content. These two
should refer to each other as follows:

@verbatim
+---------------+     +----------------+
|   TabLabel    |     |       Tab      |
+---------------+     +----------------+
|            id |<----| aria-labeledby |
| aria-controls |---->|             id |
+---------------+     +----------------+
@end verbatim

Further information about tabs in HTML can be found here:
@url{https://developer.mozilla.org/en-US/docs/Web/Accessibility/ARIA/Roles/Tab_Role}

@defvr {CSS Variable} {--tabcount}
Each tab element has the style property @code{--tabcount} set to how
many tabs it has. This is mostly useful to make sure the tab context
is large enough to fit all tab labels without overflowing.
@end defvr

@deftypemethod TabGroupElement void addTab {HTMLElement} {label: string?} {title: string?}
Adds a new tab to the group. The first parameter will make up the body
of the tab. The label is whath should be shown in the tab selector,
but defaults to the first letter of the text content of the body node.
Title is the hoover text of the label.
@end deftypemethod

@deftypemethod TabGroupElement void removeTab {HTMLElement}
HTMLElement must be one of the tab bodies in this group. This method
removes it, along with its TabLabel.
@end deftypemethod

@end deftp