I’ve been using PlantUML for my technical diagrams recently; the ability to include the source for my diagrams along side my projects has been a documentation game changer.

The tool is pretty well documented on their website but a few things are not immediately clear until you stumble with using it a few times.

How do I pick the diagram type?

PlantUML doesn’t have an documented mechanism for defining the type of diagram you are trying to generate. Defining a node type element tells PlantUML to generate a component diagram.

In my use case, I was trying to create a sequence diagram but I accidentally created an element of type component. This caused my diagram to default to a Component diagram, which doesn’t support the group feature; this was present in my diagram’s definition but was causing a syntax error I couldn’t understand until I realized it’s not in the grammar for a Component diagram.

The solution was to replace the node with boundary and control elements.