diff --git a/doc/coding_style.dox b/doc/coding_style.dox
--- a/doc/coding_style.dox
+++ b/doc/coding_style.dox
@@ -38,7 +38,7 @@
 
 
 \warning In some cases we diverge from these rules.
-This primary done because STL uses different naming convention and
+This is primary done because STL uses different naming convention and
 in certain cases
 it is beneficial to provide STL compatible interface.
 
@@ -95,6 +95,14 @@
 all_lower_case_with_underscores 
 \endcode
 
+\subsection pri-loc-var Private member variables
+
+Private member variables should start with underscore
+
+\code
+_start_with_underscores
+\endcode
+
 \subsection cs-excep Exceptions
 
 When writing exceptions please comply the following naming conventions.