in the database. Closes #16304 [ci skip]

Docs: Add a note on custom validation contexts. [ci skip]

Fix underscore inflector handling of namespaced and adjacent acronyms

Use #tr instead of #gsub where possible

I suspect that positive lookbehind would have been used in the
original implementation had it been available in supported Ruby
versions at the time. Now that Rails requires Ruby 1.9.2 or above,
this is no longer an issue.

This fixes #14146 for acronyms such as APIRESTful. This technique also
addresses namespaced acronyms that are not entirely uppercased. This
was broken when the commit was originally written but has since been
fixed in ccbb4819. The latter does not deal with adjacent acronyms so
this commit wins.

fix typo in in define_model_callbacks comment [ci skip]

Fix typo [ci skip]

add notes for `define_model_callbacks`

define hash on duration

Reason: There is a wrong newline, a typo, and the change
to singular is not good.

This reverts commit d76380cf.

[Railsguides] Fix style for rescue responses doc [ci skip]

[ci skip] add `test:jobs` task to testing guide

 * Change 'Any ***s that are...' to 'Any *** that is...'
 * Fix style for default rescue_responses setting

This is a follow-up commit to:

 * https://github.com/rails/rails/pull/17076
 * https://github.com/yuki24/rails/commit/89b8836f2470c689f6b7d52cab3a418bb63aef26

Disallow appended newlines when parsing as integer

\Z allows appended newlines where \z does not.

[ci-skip] Update Active Job API documentation

This adds documentation for the Active Job API. It includes
documentation on how to configure the queue_adapter, and how to create
new jobs. It adds links to the various other sections of the Active Job
documentation.

Follow up to #16613

use tr instead of gsub when possible

In render file, by default the current layout is rendered always [ci skip]

Added processing of `nil` to `highlight` helper method

Refactor callback setup to use lambda instead of eval

It is temporary until we do the final release

Update single table inheritance link anchor

The current one is old-of-date and doesn't make the browser navigation to the correct heading.

Remove RUNNING UNIT TESTS from ActionPack

[ci skip]

Following discussion with @senny https://github.com/rails/rails/pull/17100#issuecomment-57285273
it only makes sense to keep this file form projects that require
extra instructions.