Use a prefix for all your commands when you want to create extension-specific commands. For example if the prefix is "myextension" and the commande "blah", the actual command to be written by the user is "myextension:blah". Give as parameter the function that will parse the command and do an action. Its first parameter is the full command as a string. The second one is the command without prefix, split by word. It must raise ocsigen_extensions.Unknown_command if it does not recognize the command.