Added handling of aria-expanded=true/false to collapse.js, updated
documentation to include advice on making expand/collapse controls
accessible, updated examples and javascript documentation to use
aria-expanded and aria-controls (when targetting single collapsible
element, using ID rather than class selector)

Closes #14147.
Closes #14153.

Remove `aria-describedby` attribute later

Ensure that hidden event is sent when content is really hidden (collapsi...

Thanks to @collinanderson
Closes #14567

Revert #13855 due to #14263

Properly hide checkbox and radio inputs in button groups

Add @hnrch02 to Core Team members list

Cleaned up fix for #14511 (input border-radii variables)

Fixes #14557: .form-group margin in .navbar-form

Fixes #14557: Reset the bottom margin on .form-group:last-child in .navbar-form to prevent extra spacing

Fixes #14319: Jumbotron reflow

[skip sauce]

Fixes #14319: Prevent jumbotron reflow by ensuring padding of .container isn't interferred with by .jumbotron side padding

`pointer-events: none;` for modern browsers (including IE11+), `clip: rect(1px, 1px, 1px, 1px);` for everything else.

Fixes #14137

If opening a modal when a scrollbar is present, closing it, then
resizing the window so the scrollbar disappears, then opening the
modal again, the content would shift. This fixes the problem by
always calculating the scrollbar width every time a modal is opened.

Closes #14357.

Fix hover-popover/tooltip flickering when mouse re-enters

Address #14541 by tweaking badge docs

Add section to docs explaining our stance on validators

* move unrelated .btn-primary example out of the pills subsection
* remove excessive .nav-stacked example

Fixed typos involving apostrophes

Added apostrophes to 3 words to indicate possession (i.e. ownership of something) instead of plurality (i.e. multiples of something).

Fixes #14500

add entry for #14528 to Wall of Browser Bugs

Add Wall of Browser bugs entry for #793