How to use the update type

[jonathanschneider]

I don't get the update type. In the Wiki under Message definition it states the following:

any other character: update
All of the remaining characters can be used to define a passive message that ebusd will listen to in order to recognize updates of field values. If the type is suffixed with a "w", the message is treated as write message as mentioned above. Otherwise it is treated as read message.

In the few configuration files that use u as type, the type was defined before with *u. If it must be defined how does ebusd know to treat it differently?
I've tried to adjust configuration files by simply using u, by combining it with r;u and wu and defining it before with *u but I can't get it to work. Either the configuration file isn't loaded at all or I don't notice any effect.

Can anyone explain to me how to use the update type?