Twenty Fifteen: Keep sub-menus open when visiting sub-menu pages

[zoonini]

A WordPress.com user who's been using Twenty Fifteen noticed that it becomes a bit cumbersome to keep re-opening a sub-menu.

To replicate:

1. Create a primary menu with sub-menu items, either through the default or custom menu
2. Visit the site on the front end and click the top-level menu item
3. Click a sub-menu item
4. Note how you need to click the top-level menu item again if you want to visit another sub-menu page in the same section

It would save some user clicks to keep the sub-menu open after it's been first clicked.

As the user puts it:

The problem is that once the user selects one of these nested items and navigates to the page, the nested menu closes again, meaning that the user has to re-click on the parent item over and over again to keep opening up the nested menu to view what other pages are under it. As you can imagine, this becomes very annoying for the user very quickly. Is there any way to customize the menu so that the nested list will stay open as long as the user is on a page that is nested under the same parent item?

Suggested ​in this forum thread.

[iamtakashi]

It could be a good enhancement but for the next update since we are so close to the initial release.

[jartes]

Just display the sub-menu for menu items that has .current_page_ancestor class.

[lancewillett]

Patch is good start. I think it also needs .current-menu-ancestor selector as well, to cover both fallback menu (pages) and custom menu.

[iamtakashi]

Twenty Fifteen doesn't have the fallback page navigation so it should be fine with using just .current-menu-ancestor.

[jartes]

In 30722.1.diff all the work now it’s made with javascript as we need to add ‘toggle’ classes to open submenus.

Also added proper 'font-weight' for .current-menu-ancestor items

[lancewillett]

I wasn't able to cleanly apply the patch -- jartes can you please refresh your patch with latest version of the theme in trunk?

[jartes]

Added refreshed patch :)

[lancewillett]

In 31214:

Twenty Fifteen: keep sub-menus open when visiting sub-menu pages, to show context when navigating a site.

Props jartes, fixes #30722.