1. A method for dynamically loading portions of a computer-aided design (CAD) model on demand, comprising: loading, by a CAD application executed by a processor of a computing device, a first portion of a CAD model in response to a request to load the CAD model, the first portion comprising (i) a first modular structure of the CAD model, (ii) graphics and geometry data of elements of the first modular structure, and (iii) a parametric constraint with respect to a second portion of the CAD model, wherein the second portion comprises (iv) a second modular structure of the CAD model, and (v) graphics and geometry data of elements of the second modular structure; responsive to an attempt by a user to modify the geometry of one or more elements of the first portion of the CAD model, determining if the modification to the one or more elements relates, at least, to the parametric constraint of the second portion and automatically loading, by the CAD application, the second portion of the CAD model if the modification relates to the parametric constraint of the second portion, wherein the automatic loading occurs without receipt of an input from the user that corresponds to a selection of the loaded elements of the second portion; and enforcing the parametric constraint between the one or more elements of the first portion of the CAD model and the loaded elements of the second portion of the CAD model.