In the explanation of Pre-Defined Parameters for UDTs it states:
UDTs have a few parameters already defined to make things easier for you. They give you access to the name and various paths associated with a UDT member Tag. These parameters can be accessed from anywhere in a Tag that a normal parameter can be used. Each of these parameters uses that Tag it is in as a starting point for its path.
These are the
- {InstanceName}
- {PathToParentFolder}
- {TagName}
- {PathToTag}
And the associated image shows these parameters used within tags in a UDT
However the next section, "Adding a Parameter to a UDT", shows adding a custom parameter to a UDT, but only uses static values for the value of those example parameters.
What it does not show (or IMHO not made clear enough) is that the value of a UDT custom parameter can also be set to any of the predefined parameters listed above. I'd suggest adding clarification to this topic about this possibility.
(And if you really wanted to get fancy you could update the editor for the custom parameters, so that it has access to the list of predefined parameters in the same manner as when editing a UDT member tag.)
My use case for this is that I want to create a UDT with 40 or 50 elements, and I want to create instances pointing to 10 to 20 different PLCs. So in my UDT I create a custom parameter called OpcConnector that has a default value of {InstanceName} and I use {OpcConnector} for the "OPC Server" field of each UDT member. Now if I create an instance of the UDT with the name of the OPC Connector for a specific PLC, then the data automagically appears. But if I want to decouple the target PLC from the Instance Name I only have to override the OpcConnecter parameter in a single location.
I only discovered this by going "I wonder .." (but I am really happy that I did discover it)