instructions: file_conventions: update section

* source/instructions/coding_style/file_conventions.rst: Here.

source/instructions/coding_style/file_conventions.rst

@@ -3,7 +3,7 @@
 File Conventions
 ----------------
 
-There are some strict conventions to obey wrt the files and their
+There are some strict conventions to obey regarding the files and their
 contents.
 
 Rule: One class :code:`LikeThis` per files :code:`like-this.*`
@@ -18,7 +18,7 @@ Rule: :code:`*.hh`: Declarations
   The :code:`*.hh` should contain only declarations, i.e., prototypes,
   :code:`extern` for variables etc.  Inlined short methods are accepted
   when there are few of them, otherwise, create an :code:`*.hxx` file.  The
-  documentation should be here too.
+  documentation should be here in the :code:`*.hh` too.
 
   There is no good reason for huge objects to be defined here.
 
@@ -45,6 +45,12 @@ Rule: :code:`*.hh`: Declarations
       Actually, if you merely need to declare the existence
       of streams, you might want to include :code:`iosfwd`.
 
+  Relevant C++ Core Guidelines:
+    - :cppcgl:`sf2-a-h-file-may-not-contain-object-definitions-or-non-inline-function-definitions`
+    - :cppcgl:`sf4-include-h-files-before-other-declarations-in-a-file`
+    - :cppcgl:`sf10-avoid-dependencies-on-implicitly-included-names`
+    - :cppcgl:`sf11-header-files-should-be-self-contained`
+
 Rule: :code:`*.hxx`: Inlined definitions
   Some definitions should be loaded in different places: templates, inline
   functions etc.  Declare and document them in the :code:`*.hh` file, and
@@ -52,6 +58,8 @@ Rule: :code:`*.hxx`: Inlined definitions
   *last* includes the :code:`*.hxx` file, conversely :code:`*.hxx`
   *first* includes :code:`*.hh`.  Read below.
 
+  Relevant C++ Core Guidelines:
+    - :cppcgl:`f5-if-a-function-is-very-small-and-time-critical-declare-it-inline`
 
 Rule: :code:`*.cc`: Definitions of functions and variables
   Big objects should be defined in the :code:`*.cc` file corresponding to
@@ -68,8 +76,7 @@ Rule: :code:`*.cc`: Definitions of functions and variables
 
     .. code-block:: c++
 
-     void
-     LetExp::accept(Visitor& v)
+     void LetExp::accept(Visitor& v)
      {
        v(*this);
      }