The message if a Flow-enabled page has an empty header is
'flow-header-empty' => 'This talk page currently has no header.'
But you can enable Flow for pages that aren't in a talk namespace, e.g. Sandbox.
If we like this language, then we could test for $this->isTalkPage() and show one of 'flow-talkpage-header-empty' or 'flow-nottalk-header-empty' messages. But since the tab is called "Discussion" and we may change it to "Board", maybe calling Flow-enabled pages "Talk" pages isn't ideal.
Version: master
Severity: minor