Merge branch '3.4' into 4.4

* 3.4:
  Enhancement: New rules for DOCtor-RST.
  [#14421] Merged the new description into the current sentence
  Adding more information about default translation domain 'messages'

Author: OskarStark

.doctor-rst.yaml

@@ -25,6 +25,8 @@ rules:
     no_namespace_after_use_statements: ~
     no_php_open_tag_in_code_block_php_directive: ~
     no_space_before_self_xml_closing_tag: ~
+    only_backslashes_in_namespace_in_php_code_block: ~
+    only_backslashes_in_use_statements_in_php_code_block: ~
     ordered_use_statements: ~
     php_prefix_before_bin_console: ~
     replace_code_block_types: ~

translation.rst

@@ -387,9 +387,10 @@ priority message files.
 The filename of the translation files is also important: each message file
 must be named according to the following path: ``domain.locale.loader``:
 
-* **domain**: An optional way to organize messages into groups. Unless
+* **domain**: Domains are a way to organize messages into groups. Unless
   parts of the application are explicitly separated from each other, it is
-  recommended to only use default ``messages`` domain;
+  recommended to only use the default ``messages`` domain (e.g.
+  ``messages.en.yaml``).
 
 * **locale**: The locale that the translations are for (e.g. ``en_GB``, ``en``, etc);