Comment 3 for bug 1417291

docs-has-sub is used in the following function in docs.js:

// Toggle 2nd sub-sections
$(".docs-sidebar-section ol > li > a").click(function () {
    $('.docs-sidebar-section ol li').not(this).removeClass('active').removeClass('open');
    $(this).closest('.docs-sidebar-section ol li').toggleClass('active');
    if ($('.docs-has-sub').hasClass('active')) {
      $(this).closest('.docs-sidebar-section ol li').addClass('open');
    }
    event.preventDefault();
});

It seems to implement a multilevel menu in the sidebar that features plus signs to indicate expandability of a collapsed menu point (and minus to indicate that an expanded menu point can be collapsed).

It's therefore not sufficient to just remove the docs-has-sub rule; instead, the implementation of multilevel menus needs to be redone so that it doesn't interfere with innocent normal lists.