Structural Modeler utilizes the new AutoCAD 2000 MDI capability to allow designers to edit several drawings simultaneously, for the first time ever. This MDI functionality (multi-document interface) is inherent throughout the application, meaning that you'll never have to load the program into memory more than once.
Using this feature, a designer can open a model in multiple drawing sessions (windows), and experiment with a variety of detailed settings in order to preview the final effects. Another application would be the ability to simultaneously edit multiple models in different drawings.