Add documentation to components/utilities to publicly expose the
.pos-f-t utility class to users.

Closes #18799
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It's very handy to add another spacer size (e.g. `4`) which can easily be done by extending the map.
Example:
```
$spacers: (
  0: (
    x:   0,
    y:   0
  ),
  1: (
    x:   $spacer-x,
    y:   $spacer-y
  ),
  2: (
    x:   ($spacer-x * 1.5),
    y:   ($spacer-y * 1.5)
  ),
  3: (
    x:   ($spacer-x * 3),
    y:   ($spacer-y * 3)
  ),
  4: (
    x:   ($spacer-x * 5),
    y:   ($spacer-y * 5)
  )
);
```

Closes #18706
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- Add/replace callout for color and AT with include

This one was overlooked at edit

See #17719 and #19199

Alternate fix to #17965: Updates to use the new class name and adds some basic docs for custom checkbox/radio validation

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Fixup for 365db6e3
/fyi @mdo
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Refs #19102
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Fixup for #19105
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- Switch from width to max-width for all widths to avoid scaling outside viewport bounds
- Rejigger the media queries for a more logical breakpoint for the large and small modal sizes
- Avoids changing the width of the default modal (nullifying #17794 and fixing #17581)

- Make it an explicit class instead of qualifying with elements (.list-group-item-action)
- Rearrange the entire file for more straightforward flow
- Fix text-decoration bug as a result of the reorder
- Switch from h4's to h5's in docs
- Update docs to merge anchors and buttons sections; clearify usage guidelines there, too
- Nullify #17479 in the process

- Both classes do about the same thing, but with different names
- Clarifies docs for .m-x-auto requiring a fixed width block element for it to work
- Add missing heading for clearfix section in docs (unrelated)

Dump the type margin overrides in alerts for utils, document that particular example, sidesteps part of #18884

Closes #19049

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see https://github.com/twbs/bootstrap/pull/18782

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Put all the textual input types right next to each other for easy visual comparison.
Refs #17308, #18763

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- More consistent states and labels in nav examples
- Add stacked pills example for with <nav> element

Refs #18708
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It has been removed from the HTML specification: https://github.com/whatwg/html/issues/336
Only Presto Opera ever implemented a special UI for it.

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/fyi @mdo

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