Indicates if this object is still valid, i.e. hasn't been deleted or some other action done to invalidate the reference.
"constructionPlaneMidplaneDefinition_var" is a variable referencing a ConstructionPlaneMidplaneDefinition object. | 
        
"constructionPlaneMidplaneDefinition_var" is a variable referencing a ConstructionPlaneMidplaneDefinition object. |