The present invention relates to systems and methods that facilitate dynamic programming language execution in a managed code environment. A class component is provided that declares an inheritance hierarchy for one or more tagged values associated with a dynamic programming language. During execution of the tagged values, a rules component mitigates user-defined types from inheriting or deriving properties from the tagged values in order to support a type safe runtime environment. A bifurcated class tree is provided that defines non-tagged type elements on one side of the tree and tagged type element values on an alternate branch of the tree. The rules component analyzes runtime extensions that help to prevent data from one component of the tree deriving or inheriting properties from another component of the tree. The runtime extensions include such aspects as cast class extensions, test class extensions, and conversion class extensions for converting data types from one class subtype to another.