Feature summary (what you would like to be able to do and where):

• Make OutputPage stores the data of the navigation bar.
• Create OutputPage::addNavigationBar(…) function to store the data.
• Make SpecialPage::outputHeader() renders the navigation bar using the data.
• Make Skin::getTemplateData() provides the data of the navigation bar. And implement features and flags for making sure the navigation bar is not duplicated.
• (Maybe another task) Provide a parser function that allows editors on the wiki to add a navigation bar to a general wiki article.

Use case(s) (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):

Some special pages provide the navigation bar(links) on the top of the page, under the title.

Contribution	AbuseFilter	Newsletter
(code)	(code)	(code)

Those pages create links and append those to the subtitle of the page. I don't know why the 'subtitle' was named, but if it just means the position, I think it is worth splitting some function of it based on the role.

Benefits (why should this be implemented?):

• Code duplications would be reduced and the same user experience over multiple special pages would be provided.
• The core and extension developers could use SpecialPage::addNavigationBar(…) instead of creating from scratch.
• The skin developers could acquire more flexibility over navigation bar render.
• (Maybe another task) The template editors could provide the same navigation page experience for Template:Sidebar.