To help classify commands, a distinction has been made. This distinction is based upon how the command is used, and what it effects. If the command is a Non-VR command (it does not follow the Virtual Environment guidelines) it begins with an at-sign ('@'). Otherwise, it does not.
The best way to decide if a command is VR or Non-VR is to ask yourself the question: Is it something I could do in real-life? For instance, you do not simply declare, "I am wearing pink polka dotted clothes", and suddenly you are. However, in the Cold Dark you have the ability to directly change how you look from moment to moment. Therefore this command (@describe) is a Non-VR command, and begins with an at-sign.
VR vs Non-VR | Types | Matching Conventions