A plug-in must implement the XSILoadPlugin callback, which is responsible for registering plug-in items such as commands and properties.
Plug-in items properties are implemented by callback functions. For example, to implement a custom command, you write an Execute callback. If the command is named, "MyCommand", then Softimage expects a callback function named "MyCommand_Execute".
If the name of a plug-in item includes spaces, you must remove the spaces from the callback function names. For example, if a property is named "My Custom Property"), then the Define callback function for the property must be named "MyCustomProperty_Define".