Hi,
can’t find any infos to this issue or limitation info (forum, stackoverflow etc.)…
Same behavior also on the vaadin demo website https://demo.vaadin.com/sampler/#ui/structure/accordion
Description on Accordion itself is working, but not on tab.
Description on TabSheet Tab works fine. https://demo.vaadin.com/sampler/#ui/structure/tab-sheet
We are using 7.7.10.
All your comments, hints and suggestions are welcome 
Cheers, Daniel
Thanks for reporting this. I think this may be a bug. I briefly checked our sampler you linked. It is possible to assign description to “Tab 5”, I did so. Description should appear as a tool tip. I see in Google developer tools that “v-caption-hasdescription” style is correctly attached and when I hove on tab, it flashes “::before”, but text is not appearing, so something is wrong. Could you enter bug report here (there seems not to be one yet)