You can change Mediawiki's left-hand nav by editing MediawikI:Sidebar et al.

https://www.mediawiki.org/wiki/Manual:Interface/Sidebar

You can insert a TOC anywhere with magic word TOC

https://www.mediawiki.org/wiki/Manual%3aTable_of_contents#Positioning_the_TOC

You can add new "divisions" (tabs) like here:

https://www.mediawiki.org/wiki/Manual:FAQ#How_do_I_add.2Fremove_tabs_throughout_my_wiki.3F

Is that true in Blueprint skin?

I _think_ these things should not change depending on which skin you are using.

@Qgil, maybe we don't need tabs for "divisions"; that was me looking at some mockups from Jared Zimmerman that linked doc.wikimedia.org, dev.wikimedia.org, and mediawiki.org.

In T93062#1397845, @Qgil wrote:

Is that [@Dzahn's explanation] true in Blueprint skin?

Blueprint works differently than other skins:

• It has its own 'MediaWiki:Blueprint-left-nav' (sample) definition for its pop-up sidebar.
• It removes the current page's TOC and inserts it into its pop-up sidebar, under the current page in the left-nav links, or at the bottom of the sidebar if the current page is not one of the left-nav links.

Blueprint currently works best when the left nav isn't too big and all pages are links in it. That won't apply for the API namespace. So we could continue to have in-page navigation for the PHP action API, or we could come up with requirements for a better Blueprint.

With only paper and pencil (or with only a textarea in this task), what is the navigation structure we need to organize all the API: namespace content, old and new? Let's solve this question first, and then we will see how can we use Blueprint and on-wiki navigation templates.

Update: I've refined the big unwieldy API navigation template to reference Web APIs hub before its big list of action API pages. I think it's OK for the Web APIs showcase pages to not have that big navigation that's mostly dedicated to the action API.

The Web APIs hub pages in Blueprint have their own navigation in the Blueprint sidebar (sample - click the top left icon). We need to decide whether to replicate this in non-Blueprint skins or push for Blueprint.

I added the {{API}} navigation template to Web APIs hub "Build" section, but collapsed. Ugly, but it adds navigation to the new front door that developers requested. A next step would be a gadget to "jump down to navigation", and/or perhaps shrink it to just
[Show action API navigation]

I added a proposal to improve the API navigation to its talk page, basically making it a proper menu bar like: