There may be a definition, but as I stated, the system has changed vastly. That is due to the addition of the Navigation Manager, which allows you to add tabs easily in the site. This was one of the most requested items in jira, so if users move to a different platform, after something they asked for, makes no sense.
Like I said, I would get your skin dev to update the style to support v4.2.1, or look on here to get a style that is for that version,
https://vborg.vbsupport.ru/forumdisplay.php?f=247