Compatibility plugins

The host banner reports whether plg_behaviour_compat or plg_behaviour_compat6 is enabled on this site.

• Joomla 4 and 5: plg_behaviour_compat still maps many Joomla 3 class names.
• Joomla 6: that plugin is gone. Use plg_behaviour_compat6.
• Classes Aliases: off by default on compat6. JFactory and friends will not load until you turn it on.
• Joomla 7: everything compat6 covers is scheduled for removal. Rewrite instead of relying on the plugin.

Finding chips (Needs aliases, Needs legacy classes, Needs asset stubs, Will not run) match those layers.