From OpenSCADAWiki
The engine of the visualization environment provides activation of the visualizer specific attributes. The activation process performs at opening a session of the project and means for the project: creation of the specific attribute with the specified properties, at case it lack, and activation for tracing its modification by the engine of the visualization environment, like to the attributes of forming primitive's shapes. To direct specifying such attribute you can also use the prefix "vs_" to the attribute identifiers, what is mach faster and excludes of the activation stage. For the specific attributes list of the visualizer you can see the documentation of the proper visualizer.