Focus opened by link module/class in sidebar

Hello!

Documentation for `Array` in Ruby [has links to other classes](https://devdocs.io/ruby~2.5/array), like `Parent` and `Included modules`.

When I go (click) on `Enumerable`, for example, I want to see it focused in the sidebar with the list of methods.

For now there remains `Array` and becomes inactive (gray).


And for list of `Enumerable` methods I have to scroll sidebar manually (or search it).

Thanks.

Reproduce the navigation from the linked Ruby Array documentation by clicking the Enumerable link and observing the sidebar. Trace the sidebar entry point responsible for focus and method-list positioning; done means the clicked class or module is focused and its methods are visible without manual scrolling or another search.

Written by the indexing model from the issue text.