docs: styleguide, establish line wrapping and $() instead of ``

doc/styleguide.txt

@@ -37,22 +37,33 @@ be more efficient in some cases and may reduce need for nesting
 conditions, and it's cleaner to write for example [[ ... && ... ]]
 than [ ... ] && [ ... ], and in general [[ ]] has more features.
 
+Line wrapping
+-------------
+
+Try to wrap lines at 72 characters. Never go past this limit, unless
+you absolutely need to (example: a long sed regular expression, or the
+like). This also holds true for the documentation and the testsuite.
+Other files, like ChangeLog, or COPYING, are exempt from this rule.
+
+$(...) vs `...`
+---------------
+
+When you need to do some code substitution in your completion script,
+you *MUST* use the $(...) construct, rather than the `...`. The former
+is preferable because anyone, with any keyboard layout, is able to
+type it. Backticks aren't always available, without doing strange
+key combinations.
+
 /////////////////////////////////////////
 case/esac vs if
 ---------------
 
-line wrapping
--------------
-
 quoting
 -------
 
 awk vs cut for simple cases
 ---------------------------
 
-$(...) vs `...`
----------------
-
 variable and function naming
 ----------------------------