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This PR was merged into the 3.2 branch.

Discussion
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Mentioned %env(...)% variables in Best Practices book

Commits
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91096ec Mentioned %env(...)% variables in Best Practices book

* 3.2: (22 commits)
  add missing config formats
  [#7224] fix indentation
  [#7220] some minor tweaks
  [#7196] add versionadded directive
  Explained how to improve the readability of long numeric literals
  Fix typo in workflow usage code lock
  Added "How to Use a Custom Version Strategy for Assets"
  Use PHP 5.5's ::class notation
  Update state-machines.rst
  [PHPUnitBridge] Fix copy/paste error
  [PHPUnitBridge] Fix copy/paste error
  [#7243] minor tweak
  Deletes duplicate "Deprecated" and adds a more explicit example.
  Accepted Suggestions
  Update 'query_builder' option
  Mentioned %env(...)% variables in Best Practices book
  Accepted suggestions in the guard documentation
  Accepted suggestions in the guard documentation
  Accepted suggestions in the guard documentation
  Update guard_authentication.rst
  ...