Previously, this read "Bootstrap doesn’t apply this automatically as it causes complications to other image formats." 

In this sentence, the number of the subject and the verb don't agree, and the word "this" is unclear.

These can be replaced by their `.text-xs-*` parallels.
This also avoids any complications from interactions between the responsive and non-responsive classes.
(e.g. `<div class="text-left text-md-right">`)

Refs #18300
[skip sauce]

[ci skip]

Admittedly wordy info dump on why we use `touch-action:manipulation`

refs https://github.com/twbs/bootstrap/pull/18051#issuecomment-156375970

Refactoring according the comments on https://github.com/twbs/bootstrap/pull/18104.
Closes #18131

[skip sauce]

Fix #17888

Docs should indicate that `_reboot.scss` uses the variables, but to see their values users would look in `_variables.scss`.

[ci skip]

Fix #17166

/cc @cvrebert

Mostly links.
Fixes #17056.

Example:
> ... SCSS variables (e.g., `@enable-gradients: true`) ...
Referenced SCSS but used the LESS syntax. Changed to:
> ... SCSS variables (e.g., `$enable-gradients: true`) ...

Closes #17114

Fix #17062

- Simpler main nav on all pages
- Back to purple masthead on homepage instead of dark graphite
- Active link styles on the main nav
- Cleaned up sidebar nav
- New docs layout name
- Homepage copy edits
- Updated bright purple docs color