Merge branch '6.2' into 6.3

* 6.2:
  [Standards] Improve code standards about exception and error messages

Author: javiereguiluz

contributing/code/standards.rst

@@ -179,6 +179,12 @@ Structure
 
 * Exception and error message strings must be concatenated using :phpfunction:`sprintf`;
 
+* Exception and error messages must not contain backticks (e.g. 'The \`foo\` option ...'),
+  even when referring to a technical element (such as a method or variable name).
+  Double quotes must be used at all time (e.g. 'The "foo" option ...'),;
+
+* Exception and error messages must start with a capital letter and finish with a dot ``.``;
+
 * Do not use ``else``, ``elseif``, ``break`` after ``if`` and ``case`` conditions
   which return or throw something;