minor #7845 Update translation_domain.rst.inc (enumag)

This PR was submitted for the 3.2 branch but it was merged into the 2.7 branch instead (closes #7845).

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Update translation_domain.rst.inc

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587cd7f Update translation_domain.rst.inc

Author: xabbuh

reference/forms/types/options/translation_domain.rst.inc

@@ -1,7 +1,9 @@
 translation_domain
 ~~~~~~~~~~~~~~~~~~
 
-**type**: ``string`` **default**: ``messages``
+**type**: ``string``, ``null`` or ``false``  **default**: ``null``
 
 This is the translation domain that will be used for any labels or options
-that are rendered for this field.
+that are rendered for this field. Use null to use the translation domain of
+the parent form or the default domain of translator for root form. Use false
+to disable translation.