Depending on the use of the created physics interfaces, the need for internal documentation (comments about implementation and for simplifying extending and maintaining the implementation) and external documentation (user documentation and context help) varies. The Physics Builder includes Comments nodes, where you can add comments about each feature for internal use. Those comments can provide information about the implementation, its benefits and limitations, any remaining issues, or ideas for future extensions. You can add a Comments node to each individual node in a physics interface, including the components that you use to create a physics interface feature (such as User Input and Variable Declaration nodes). By default, the preferences are set up so that a Comments nodes labeled Developer Comment appear under the nodes in the interface that needs comments.