[DOC] fixed missing doc

src/modules/arbitraryPlane/WMArbitraryPlane.h

@@ -218,6 +218,9 @@ private:
 
     static const int m_maxNumberOfTextures = 8; //!< We support only 8 textures because some known hardware does not support more texture coordinates.
 
+    /**
+     * Node callback to change position and appearance of the plane within the OSG thread
+     */
     class SafeUpdateCallback : public osg::NodeCallback
     {
     public: // NOLINT