Great to be able to actually answer my own question. RTFM.
From the CHM:
Changing Element Appearance Using Tagged Values
Some tagged values directly affect the appearance of the elements that they apply to. There follows a list of these tagged values:
· Events. To change the decoration of a Start Event or Intermediate Event, set the Trigger tagged value. To change the decoration of an End Event, set the Result tagged value.
· Gateways. To create the different varieties of Gateway, set the GatewayType tagged value. Other display options are available for XOR gateways: you can set the XORType tagged value to create Event-based or Data-based XOR gateways; and for Data-based XOR gateways you can set the MarkerVisible tagged value to false to hide the decoration.
· Activities. There is a wide variety of appearance options for Activities:
· The ActivityType tagged value can be set to Task or Sub-Process. The latter option will display the "plus-in-a-box" decoration on the bottom edge of the shape.
· An ad-hoc activity is shown by setting the AdHoc tagged value to true. This will display the tilde decoration on the bottom edge of the shape.
· A compensation activity is shown by setting the IsCompensation tagged value to true. This will display the rewind icon on the bottom edge of the shape.
· A multiple instance activity is shown by setting the LoopType tagged value to MultiInstance. This will display the pause icon on the bottom edge of the shape.
· A loop activity is shown by setting the LoopType tagged value to Standard. This will display the loop icon on the bottom edge of the shape.
· A transaction is denoted with a double-lined border on setting the IsATransaction tagged value to true.
· Sequence Flows. Setting the ConditionType tagged value to Default will put a diagonal slash across the line at the source end; Setting the ConditionType tagged value to Expression will put an unfilled diamond-shaped decoration at the source end.
· Data Objects. The value of the State tagged value will be displayed in square brackets under the object name.
Additional Tagged Values
The following tagged values are additional to or differ from the attributes defined in the BPMN Specification:
· Sequence Flows. The GatewayOrdering tagged value of Sequence Flows is functionally equivalent to the Gates attribute defined for Gateway elements in the BPMN Specification. Rather than provide an ordered list of flows in the Gateway's attribute, it is thought easier to provide an ordering value for each individual sequence flow. The first to be evaluated should have the value 1 on so on. The default flow may be left blank.
