Add "variables" section

notes/style.md

@@ -277,8 +277,59 @@ Common language constructs
 --------------------------
 
 
-### functions ###
+### variables ###
+
+Common advice applies to variable naming, but capitalization is decided
+based on scope:
+
+ *  Global variables must be `ALL_CAPS`.
+
+ *  Local variables must be `lowercase` or `snake_case`, and *must not*
+    be used in inherited scope, i.e. in a child function.
+
+ *  Optionally an exception from the previous rule can be granted to
+    a specific variable.  However, such variable must be named using
+    `CamelCase`.
+
+ *  Both kinds of local variables (inherited and non-inherited) should
+    be defined in header of the function, that is, before actual code.
+    It's also recommended to comment variables here.
+
+For example:
+
+    #
+    # My global variable
+    #
+    PLANET_NAME=Earth
 
+    main() {
+        local name=$1       # name to greet
+        local TimeOfDay     # morning, afternoon or night
+        TimeOfDay=$(determine_timeofday)
+        greet "$name"
+    }
+
+    greet() {
+        #
+        # Greet user $1 based on $TimeOfDay
+        #
+        local name=$1       # name to greet
+        case $TimeOfDay in
+            morning)    echo "Good $PLANET_NAME morning, $name!"   ;;
+            afternoon)  echo "Nice $PLANET_NAME afternoon, $name!" ;;
+            night)      echo "Sleep well, $name!"                  ;;
+        esac
+    }
+
+    main "$1"
+
+Notice that while `TimeOfDay` is allowed to slip through and be referenced
+in `greet()`, `name` is purely local to `main()`, and then again to
+`greet()`.  (It's probably not a good idea to mix variables like that,
+the example is ugly, but you get the point.)
+
+
+### functions ###
 
 Preferred way of declaration is a variation of most common Bourne shell
 way with K&R-style brackets: