…t, javiereguiluz)This PR was submitted for the 3.2 branch but it was merged into the 2.7 branch instead (closes#7664).Discussion----------Add an explanation about «constraints» validationAdded an explanation about the use of «constraints» in Form Classes and the requirement of «ValidatorExtension» if «constraints» keyword is used.This is currently not explained in doc, nor in Forms, Validation, Custom validation or any other page.Commits-------c9f1b95 Rewords and minor fixescb6b2e6 Add an explanation about «constraints» validation

* 2.7: (31 commits)  Fixed the RST syntax  Improve example context  [#5621] Enhancing example of using bundle config  [#7601] minor tweak  Update expiration.rst  Update expiration.rst  Update expiration.rst  Update expiration.rst  Minor reword and fixed the line length  Improve specification explanation  [#7664] minor wording tweak  Rewords and minor fixes  Add an explanation about «constraints» validation  [#7645] enumerate ordered list items implicitly  Adding a new article about "Creating a Bug Reproducer"  Fixed a syntax issue  Use backticks#7311 choice_value callback argument can be null  Fixed broken links for nginx & FastCgiExternalServer  Update dialoghelper.rst  ...

* 2.8: (46 commits)  [#7507] fix component name  [#7490] minor typo fix  Added a note about redirections to absolute URLs in tests  Added the changes suggested by reviewers  [#7620] use generate() in PHP templates before 2.8  Fixed the RST syntax  Improve example context  [#5621] Enhancing example of using bundle config  [#7601] minor tweak  Update expiration.rst  Update expiration.rst  Update expiration.rst  Update expiration.rst  Minor reword and fixed the line length  Improve specification explanation  [#7664] minor wording tweak  Rewords and minor fixes  Add an explanation about «constraints» validation  [#7645] enumerate ordered list items implicitly  Adding a new article about "Creating a Bug Reproducer"  ...