9. A method of enforcing constraints in a computer-aided design (CAD) system, comprising: creating, via a parametric modeling user interface of a CAD application executed by a processor of a computing device, a parametric history-dependent feature constraint of a CAD object, the CAD object comprising an historic instruction list of feature-based geometry of the CAD object such that modification of an earlier-created feature in the instruction list causes a parametric geometry engine to recalculate later-created geometric features to carry through the effects of the change to the earlier-created feature; attempting to modify, via a direct modeling user interface of the CAD application, the CAD object, wherein the direct modeling interface is configured to allow modification of the CAD model based on added geometry features agnostic of all associative geometric relationships within the CAD object; enforcing, by a parametric modeling engine of the CAD application, the feature constraint in the direct modeling user interface, responsive to an attempt to modify the geometry via the direct modeling user interface; preventing or rejecting, by the parametric geometry engine, the attempted modification to the CAD object, responsive to the attempt to modify the geometry; and allowing, by the parametric geometry engine, a user to override or modify the feature constraint in the direct modeling user interface.
9. A method of enforcing constraints in a computer-aided design (CAD) system, comprising: creating, via a parametric modeling user interface of a CAD application executed by a processor of a computing device, a parametric history-dependent feature constraint of a CAD object, the CAD object comprising an historic instruction list of feature-based geometry of the CAD object such that modification of an earlier-created feature in the instruction list causes a parametric geometry engine to recalculate later-created geometric features to carry through the effects of the change to the earlier-created feature; attempting to modify, via a direct modeling user interface of the CAD application, the CAD object, wherein the direct modeling interface is configured to allow modification of the CAD model based on added geometry features agnostic of all associative geometric relationships within the CAD object; enforcing, by a parametric modeling engine of the CAD application, the feature constraint in the direct modeling user interface, responsive to an attempt to modify the geometry via the direct modeling user interface; preventing or rejecting, by the parametric geometry engine, the attempted modification to the CAD object, responsive to the attempt to modify the geometry; and allowing, by the parametric geometry engine, a user to override or modify the feature constraint in the direct modeling user interface. 11. The method of claim 9 , wherein the feature constraint comprises a geometric constraint.