Refs #15998
Effectively reverts #16473
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Refs #15205, #15407
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Refs #15846, #15832
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Refs #16813, #16809
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Also, include visible <label> as a suggestion in the accessibility
callout.

Closes #16773 by merging a tweaked version of it.
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They're no longer on Folsom St.

Fix #16755

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Per https://github.com/twbs/bootstrap/issues/16671#issuecomment-115161001
Refs #16689
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Closes #15968.
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Closes #16671
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X-Ref #13969

Fix #16632

to include a note about `role="document"`

Initial fix to generalise use of modals. Generally, true role="dialog"
containers would require only forms/controls as content, with all other
text correctly and explicitly associated via
aria-labelledby/aria-describedby and similar...but as authors use modals
also as generic overlays, this extra role is required to get AT
(particularly NVDA) out of "forms" mode and reenable reading keys

Closes #16599 by merging a tweaked version of it.

as role="menu" is a very specific (and strict) ARIA pattern for
desktop-like application menus, and our dropdowns are often used
as pure navigation dropdowns, this change abandons ARIA menus for
a more open-ended and light-weight approach
(see http://heydonworks.com/practical_aria_examples/#submenus and
http://www.w3.org/WAI/tutorials/menus/flyout/#improve-screen-reader-support-using-wai-aria)
note that in dropdown.js, switched to now target ``.dropdown-menu``
instead of ``role["menu"]`` - this also prevents bootstrap scripts
from "bleeding" into non-bootstrap components on the same page.
also removed the ``role=["listbox"]`` part, which appears to be
vestigial/unused (only place in bootstrap that uses that
role are carousels, and their key handling is done separately)

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[Close #16441] ScrollSpy requires non-body elements to have height and padding

The .container that immediately surrounds .carbonad has a padding of 15px, not 30px.

Fixes #16552.

http://www.w3.org/TR/wai-aria/roles#separator

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Closes #15016.

[Close #16502] Clarify the bs-callout on multiple open modals

Currently it states overlapping modals, this isn't the only case as this truly applies to any instance when a user would want to open multiple modals at the same time. For this reason, I have modified the title of the callout to make this more clear.