Menuitem Subtitles (multiline)
With this JYAML feature you can add additional text lines (subtitles) in the menuitem settings.
The advantage of this method is that no extension must be adjusted for it. Page-titles or e.g. the pathway (breadcrumbs) module remains of the original menu title.
The navigation stylesheets are designed to be filled on a horizontal view of all other menu items with a corresponding number of blank lines. So that the height is equal. On vertical view the blank line will be hidden. Of course this can be changed individually. For this look in the appropriate navigation.*.css stylesheets.