Explicit route test class

shows the class that the test must extend in order to have the assert_routing method available
FileHandler should not be called for files outside the root

FileHandler#matches? should return false for files that are outside the
"root" path.
If Rails is not defined, check ENV["RAILS_ENV"] and ENV["RACK_ENV"].

This fixes a regression introduced by 6cc03675d30b58e28f585720dad14e947a57ff5b.

ActiveRecord, if used without Rails, always checks the "default_env" environment. This would be OK, except that Sinatra also supports environments,
and it runs with {RACK|RAILS}_ENV=production. This patch adds a fallback to RAILS_ENV and RACK_ENV (and ultimately default_env) if Rails.env doesn't exist.
[ci skip] Add missing blank line to AR validation.
[ci skip] No need to indent here (AC overview).
[ci skip] Add highlight to code (form helper guide).
Make `String#remove` and `String#remove!` accept multiple arguments
Remove redundant `to_s` in interpolation
Merge pull request #17434 from claudiob/remove-redundant-to-s

Remove redundant `to_s` in interpolation
Use `#between`, rather than `#in` for passing Ranges to Arel

Passing ranges to `#in` has been deprecated in Arel.
Remove redundant `to_s` in interpolation
Add :db_runtime to table [ci skip]

It was missing from table, but is present in sample hash below
Merge branch 'strzalek-asn-docs-fix'
Add status code to AS::Instrumentation table, like #17441 [ci skip]
Merge branch 'master-sec'

* master-sec:
  FileHandler should not be called for files outside the root
Merge pull request #17440 from claudiob/remove-yet-another-redundant-to-s

Remove redundant `to_s` in interpolation
Use released arel
Prepare for 4.2.0.beta4 release
[ci skip] fix incorrect key in Active Support Instrumentation guide
Merge pull request #17451 from y-yagi/fix_asi_guide

[ci skip] fix incorrect key in Active Support Instrumentation guide