Refs https://code.google.com/p/chromium/issues/detail?id=544290
Refs https://bugs.webkit.org/show_bug.cgi?id=150271
Closes #17913
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Since `aria-label` is used, it's not necessary anymore.

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See https://bugs.webkit.org/show_bug.cgi?id=150079
Closes #14975
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See http://trac.webkit.org/changeset/190893
Refs #9774, #14907
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Fix #17888

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https://bugs.webkit.org/show_bug.cgi?id=149935
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See https://github.com/twbs/bootstrap/pull/17793#issuecomment-146960473

https://code.google.com/p/chromium/issues/detail?id=534750
Closes #17438
Closes #14237
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The table includes a border between the two making this unnecessary

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add flexbox to the not supported list 

https://github.com/twbs/bootstrap/issues/17802

Fixes potential problems with iOS9's new viewport behavior - see for
instance https://forums.developer.apple.com/thread/13510

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Remove http://bugzil.la/1048279 entry from Wall of Browser Bugs
https://bugzilla.mozilla.org/show_bug.cgi?id=1048279 has been closed as WONTFIX.
Refs #14124.
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Changes grid and container sizes to `px`, as the
viewport pixel size does not depend on the font size.

The actual em values were inconsistent with the docs,
while the docs were not the same as the comments:

* `sm` breakpoint was 34em (544px) not 480px.
* `lg` container max-width was 60rem (960px), less gutter than `md`.
  Changed to 940px, same as Bootstrap 3.
* `xl` container max-width was 72.25rem which is 1140px not 1156px.
  Changed to 1140px matching the comment but not the docs.

Addresses #17070 and #17388.

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Closes #17699

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