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redo some dropdown docs

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Mark Otto 2017-05-30 13:59:33 -07:00
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docs/4.0/components/dropdowns.md
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@ -10,24 +10,19 @@ toc: true
Dropdowns are toggleable, contextual overlays for displaying lists of links and more. They're made interactive with the included Bootstrap dropdown JavaScript plugin. They're toggled by clicking, not by hovering; this is [an intentional design decision.](http://markdotto.com/2012/02/27/bootstrap-explained-dropdowns/)
Things to know when using the dropdown plugin:
Dropdowns are built on a third party library, [Popper.js](https://popper.js.org), which provides dynamic positioning and viewport detection. Be sure to include [popper.min.js](https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.9.9/umd/popper.min.js) before Bootstrap's JavaScript.
- Dropdown rely on the 3rd party library [Popper.js](https://popper.js.org) for positioning. You must include [popper.min.js](https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.9.9/umd/popper.min.js) before bootstrap.js in order for dropdowns to work!
- Popper.js handle natively the flip of Dropdown when it's outside the viewport, if you want to disable that's behavior use `flip` attribute
## Examples
Wrap the dropdown's toggle (your button or link) and the dropdown menu within `.dropdown`, or another element that declares `position: relative;`. Dropdowns can be triggered from `<a>` or `<button>` elements to better fit your potential needs.
{% callout info %}
### Dropdown menu accessibility
## Accessibility
The [<abbr title="Web Accessibility Initiative">WAI</abbr> <abbr title="Accessible Rich Internet Applications">ARIA</abbr>](https://www.w3.org/TR/wai-aria/) standard defines an actual [`role="menu"` widget](https://www.w3.org/TR/wai-aria/roles#menu), but this is specific to application-like menus which trigger actions or functions. <abbr title="Accessible Rich Internet Applications">ARIA</abbr> menus can only contain menu items, checkbox menu items, radio button menu items, radio button groups, and sub-menus.
Bootstrap's dropdowns, on the other hand, are designed to be generic and applicable to a variety of situations and markup structures. For instance, it is possible to create dropdowns that contain additional inputs and form controls, such as search fields or login forms. For this reason, Bootstrap does not expect (nor automatically add) any of the `role` and `aria-` attributes required for true <abbr title="Accessible Rich Internet Applications">ARIA</abbr> menus. Authors will have to include these more specific attributes themselves.
However, Bootstrap does add built-in support for most standard keyboard menu interactions, such as the ability to move through individual `.dropdown-item` elements using the cursor keys and close the menu with the <kbd>ESC</kbd> key.
{% endcallout %}
## Examples
Wrap the dropdown's toggle (your button or link) and the dropdown menu within `.dropdown`, or another element that declares `position: relative;`. Dropdowns can be triggered from `<a>` or `<button>` elements to better fit your potential needs.
### Single button dropdowns
@ -491,14 +486,12 @@ Add `.disabled` to items in the dropdown to **style them as disabled**.
## Usage
Via data attributes or JavaScript, the dropdown plugin toggles hidden content (dropdown menus) by toggling the `.show` class on the parent list item.
Via data attributes or JavaScript, the dropdown plugin toggles hidden content (dropdown menus) by toggling the `.show` class on the parent list item. The `data-toggle="dropdown"` attribute is relied on for closing dropdown menus at an application level, so it's a good idea to always use it.
{% callout info %}
On touch-enabled devices, opening a dropdown adds empty (`$.noop`) `mouseover` handlers to the immediate children of the `<body>` element. This admittedly ugly hack is necessary to work around a [quirk in iOS' event delegation](https://www.quirksmode.org/blog/archives/2014/02/mouse_event_bub.html), which would otherwise prevent a tap anywhere outside of the dropdown from triggering the code that closes the dropdown. Once the dropdown is closed, these additional empty `mouseover` handlers are removed.
{% endcallout %}
Note: The `data-toggle="dropdown"` attribute is relied on for closing dropdown menus at an application level, so it's a good idea to always use it.
### Via data attributes
Add `data-toggle="dropdown"` to a link or button to toggle a dropdown.