As an author, I would like to add tabbed content with minimal effort. Currently, it is possible to add tabbed content using the macros for the online style only, which means I need to have a fallback for offline style with "if defined" blocks. A qdoc command makes it easier to add such content, and avoids the need to use "if defined" blocks.

The new command should let me do the following:

• Add group of tabs than the reader can switch between.
• Define labels for each tab in the group and choose a default/active tab.
• If a page has several tab groups, where the labels are the same. For example, several tab groups showing snippets for signal slots in C++ and Python under different scenario, selecting one label in a group should also switch to the same label in all the groups on that page.

Other good to have features are:

• Limit the no. of tabs in a group. Not sure what would be correct no. of tabs, lets go with 6 for example.
• Choose between different style of tabs. For example, different background color or image using a config option.

A proper implementation must also take other output formats than HTML into account; see e.g. https://codereview.qt-project.org/c/qt/qtbase/+/613771 for context.