merged branch bschussek/issue3539 (PR #3898)

Commits
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2e5182f [Form] Clarified the CHANGELOG entry about the activation of addXxx()/removeXxx() methods

Discussion
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[Form] Clarified the CHANGELOG entry about the activation of addXxx()/removeXxx() methods

CHANGELOG-2.1.md

@@ -251,8 +251,8 @@ To get the diff between two versions, go to https://github.com/symfony/symfony/c
  * the radio type is now a child of the checkbox type
  * the collection, choice (with multiple selection) and entity (with multiple
    selection) types now make use of addXxx() and removeXxx() methods in your
-   model. For a custom, non-recognized singular form, set the "property_path"
-   option like this: "plural|singular"
+   model if you set "by_reference" to false. For a custom, non-recognized
+   singular form, set the "property_path" option like this: "plural|singular"
  * forms now don't create an empty object anymore if they are completely
    empty and not required. The empty value for such forms is null.
  * added constant Guess::VERY_HIGH_CONFIDENCE