def demo_boundaryFillFeatures_add(rootComp: adsk.fusion.Design.rootComponent):
# Have the two bodies selected.
filter = adsk.core.SelectionCommandInput.Bodies
body1 = _ui.selectEntity('Select tool body 1', filter).entity
body2 = _ui.selectEntity('Select tool body 2', filter).entity
# Create an ObjectCollection to use the bodies as tools.
tools = adsk.core.ObjectCollection.create()
tools.add(body1)
tools.add(body2)
# Create the input object to provide the required input.
boundaryFills = rootComp.features.boundaryFillFeatures
input = boundaryFills.createInput(tools, adsk.fusion.FeatureOperations.NewBodyFeatureOperation)
# Arbitrarily specify the first volume as selected.
input.bRepCells.item(0).isSelected = True
# Create the boundary fill feature.
boundaryFill = boundaryFills.add(input)